Struggling to decide how much suspension is needed.

You need test rides.

I have a 150/160 bird AM9. It can go anywhere (it's much better down the first bill WC track than DH bikes were BITD).

I also have a hardtail. It gets alot of use as it's more engaging than my bouncy bike.

If I had one bike, it would be a 130/140, but it wouldn't be as good (as much fun) on big stuff.

Get the bike that suits 90% of your actual riding, not the 10% that you do/hope to do. Sounds like a short travel one should fit the bill best, modern bikes are also surprisingly capable on bigger stuff too without needing loads of travel 

I have a 140/130 and a 160/150 bike and it's the lighter wheels and fast rolling tyres on the smaller bike that makes it feel different rather than the suspension .

I'd rather take a bit less travel with good geometry than the other way round but that genius does have the fancy shock to balance it out , maybe run it with some lighter tyres for local stuff then put on some meatier tyres for the lakes . Failing that which one is the best colour 😃

I know we all have different riding preferences, but when I was working in Norwich I used to ride Thetford a couple of times a week, my 160mm travel bike was a bit of a chore around there. I also had a fuel ex with 140mm travel, that was ok but I’d have preferred less travel and lighter weight. Most of my rides I used a hardtail with 140mm, I would have thought a lightweight 120mm XC full sus would be the best bike for your location?

You are probably right in your beliefs. 

You should test both to help decide. otherwise you’ll always be wondering ‘should I have gotten the other one’?

I’ve found a 150/140 Canyon Spectral fine for all my riding for the past 10 years, or thereabouts. But am going a bit bigger with 160/150 on my next one for the skills compensation. Should be plush for most Peak/Wales/Lake District stuff I do. Will be a bit OTT for the canal and gentle stuff, but there’s a hardtail for that. And it should be sweet for that ‘10%’ at parks and abroad.

I have a Spark 910 (built as a ST essentially with a 140 34 out front)
I have a Bold Linkin 150 in place of a Genius 910 ST (supply timeframe swap)
If you're talking about a full HMX framed sub 30lb Genius ST tuned then it'd be a harder choice. But if you're looking at the Genius in 910 spec level or below, then I wouldn't choose that over a spark, unles syou have BPW, alps trips annually and no otehr bike option
The 910 spark is the sweet spot that gives a full carbon frame, yes its hmf carbon but the alloy rear end on the lower spe bikes adds close to a pound, and simply dont ride as nicely.

Assuming you're looking at sales bikes.. Look for Spark 910 ST, the TR denomination just denotes the newer AXS (aside from nude x rear for 2025 models IIRC)

The last generation Genius HMX as a 160/150 bike at 29lbs was a bike I could've had as my only bike. But even here in Squamish, with the reality that I'm not riding Remy lines or the Tour de Gnar, then for the realities of what I currently ride, I'd keep my spark (plus a nude X).
The spark makes me feel like a rockstar regardless of my shitty fitness.. The Bold (or anything heavier than 30lbs with big tires, its just a mostly anticlimactic ride these days waiting to find time to get fit and get it back into the terrain I should be riding in on without worrying about crash consequences as the ridiculous speeds a 160/150 bike will give you.

Last time I had this quandary, I ended up drawing lines on a piece of paper the length of the various travel options. Helped me realise there's little difference between them.

Now, travel might influence the design intention, geometry and weight, but the travel itself isn't that important unless you're at the pointy end of the stick and need everything optimised.

I test rode a few and bought the Airdrop Edit. Because is was 160/162? No, because I had lots of fun riding in in my local terrain. Having said that, I'll also ride my 120 hardtail on the same stuff, so overall, I guess that tells you everything, or nothing.

A 120mm bike would be more suited for the XC stuff. 

Too much and it'll be a heavy bike for flat areas.

I went from a 140/130 bike to a 120/120 bike and find it much more capable and fun. It's also a couple of kg lighter so really noticeable on fast pedally single track stuff. Both bikes have been to BPW and still prefer the 120mm bike. 

For me in NW England, I've settled on 140mm rear / 160mm front at the moment.

For you in East Anglia, the Spark should be an easy choice IMO.

Modern short-travel bikes can easily cope with proper hills, for those occasional visits to the Lakes or Peaks. And it'll be so much better for the home trails.

Short travel one and some chunkier tyres for trips away. 

I live near Woburn which is a fair bit hillier than Thetford and a 240 forked hardtail is what I ride most,  the big bike is great for trips away, buy with 2.6 tyres the hardtail is pretty good even in Wales, Peaks etc

Good shout on separate wheels/tyres

I’d rather have a hardtail for that! But if you want rear suspension then I’d go shorter, purely for how much more fun it feels on less gnarly trails.

I don’t know a lot about those Scotts’s because I’ve never had one / ridden one.

But I rode a 140/130 (and later I upped the fork to 150) Bird Aether 7 for a few years - and it was ridiculously capable. Rode well at BPW / Dirt Farm - but wasn’t a chore on easily trail centre stuff like Swinley. 

Literally the only place I wished I had more travel was Antur Stiniog - and would assume I’d have felt the same at Dyfi Bike Park. Other than that it just handled everything well - natural tech / steep tech / fast and flowing trail centres etc.

From your detail of where you ride it feels like that sweet spot of short ish travel / relatively light / decent geometry is what would work well.

So the Transition Sentinel / Trek Top Fuel / Spec Epic Evo type things. If one of the Scott bikes you’re looking at has a similar sort of ride to those bikes then go with that. 

Note I now ride a big with more travel (160 front / 155 rear) slacker geometry / longer wheelbase / grippier tyres and I love it - but it would probably be a bit of a chore to pedal regularly around some of the places you mention. Epic at Dyfi Bike Park or through loads of choppy rocks at speed etc - but it sounds like you’ll rarely be doing stuff like that. 

I'm based in East Anglia and find my Hightower with 150/135 is probably as close to the 'one bike for all' sweet spot as you can get. It gets ridden at Thetford/Chicksands/Woburn with an annual Wales trip for uplift at BPW/Dirt Farm, and it never feels a chore to pedal or underbiked for the uplift stuff. If/when I ever replace it I might be tempted to up the travel a bit, as when I bought it it really was my only bike, but I now have a gravel bike as well for the local bridleway bimbling that it used to also be used for.

Thetford, swinley, lakes and the peaks were all awesome on my 120/110mm orange segment.

Thetford was less awesome on my 160/135mm geometron, it's better than the segment in the lakes and peaks.

If that was me I should go for the shorter travel. I have a 160mm hardtail and that's my version of shorter travel. 

The will both be fine. Get the one with the best paint job 🙂. There is no perfect answer, both are a good answer 

Vorsprung has some interesting thoughts on this topic which might help answer your question.

Get the bike that suits 90% of your actual riding, not the 10% that you do/hope to do.

Totally agree 100% but that can be difficult if you've only got one ring bike to rule ride them all. Definitely correct to choose the bike best suited to the majority of your riding rather than overspending for the e.g. annual Alps trip. Yes, I've been guilty of that, sure I'm not alone in that 😀 

Unless your Lakes rides are going to lots of steep tech, then I always did fine with 140mm. Get a shock you can lock out and it will be OK in the flatlands.

Thanks all for the responses, I know the Spark is the right choice although still somewhat pondering a hardtail too. I'll keep pondering and who knows what I end up with..... 

 I’m in Bedfordshire nearish to Woburn.

I mainly ride my gravel bike. I have a Fs 130mm front and rear.  It feels great on local trails. At home at say Llandegls. In the Lakes and Peak there are a few places where we’re have felt out of depth. Possibly flex as much as lack of travel. But for me that’s like 5 km of riding in 4500km

 But if i was buying again I’d go for similar travel