Groupset Choices

I'm only on 10sp but the XTR is noticeably better than the XT it replaced.
Whether that's because it's actually better or because I put new cables in when I swapped the mech and shifter I don't know🤣
The cassette is loads lighter though

If you're not going electronic, "SLX and keeping the extra cash" 👍

Slx with the XT shifter and XTR chain works superbly for me (shifter gives you double click on upshifts, and the chain apparently lasts longer)

Am I just as well off with SLX Deore and keeping the extra cash in the bank?

Yes

I’ve xt on one bike and deore on another. In all honesty other than being able to double downshift on the xt they both work as well as each other. As bits of the xt wear out or break it will be replaced with deore

M9100 XTR is bloody brilliant, chains last forever, like 1800km of long time. I've had mine fitted for nearly 3 years and in nigh on 3000km I've not even had to adjust the gears once, not even the tension and it runs sweet as a nut. If you do go Shimano get an XTR chain as they last roughly twice as long as an XT and at least 3 times as long as a SLX

XTR is lovely. But it’s spendy and not necessary more durable.
If you can afford it and maintain it is great.

Plenty of other viable options tho.

Currently looking at building up a new flat-bar do it all bike and undecided about groupsets.

My thinking would be that my do-it-all bike gets more abuse than anything else I ride, so why would I even be thinking about putting a top of the range, very expensive groupset on it just to leave outside the pub/outside the shops/covered in mud?

But, if you can afford XTR and are happy with the way that you are likely to treat it it's your choice.

imho....
GX casette + chain...
XT mech...
XTR shifter....

'probably' best bang for buck....
I do prefer XD to micro spline, and have broken so many sram mechs that its not worth going there...
Why, oh why, when Shimano decided to completely re design their cassette free body to accept a 10t they stuck with the squeeze more cogs on by having them separate, and then the smallest cogs fitting onto the next smallest one etc... I do not know.
I get it, trying to add 8, 9 10 and 11 onto the same FH standard its making it work with what exists, but when starting from the ground up again... it just feels like a job not done properly....

Personally I don’t like Shimano 12 speed chains - when they get wet / muddy etc they are noisy and skip about a bit. Sram 12 speed chains don’t do this on exactly the same xt cassette / shifter / northshore billet chainring (meant for Shimano chains) - they just continue running sweetly. Plus oil slick / gold colours available for the bling. Last ages and ages too.

So if money is no object I’d go Xtr cassette (very light), Sram XX1 chain and then whichever mech a
/ shifter you fancy.

I’ve heard the deore mechs don’t last as well, and the slx jockeys have bushings that aren’t brilliantly durable - so XT or XTR.

On cranks it’s up to you how bling you want to go. HT2 are probably the most durable bb’s but the Shimano cranks aren’t wildly light.

Am I just as well off with SLX Deore and keeping the extra cash in the bank?

Deore FTW (maybe with a posh XT shifter, if you are feeling spendy)

XTR shifter
XT mech
XT cassette
XT chain

SP41 gear cable inner and outer, everything else is shit in comparison.

XTR cassettes are light, but not the durable, I have one for the summer on the stumpy.

XT cassettes and cranks have always been on my bikes for as long as, same with the shifter but occasionally upgraded to XTR pod, I also wish Shimano would make the smaller cassette cogs a one piece cluster, the freehub scarring has always come from the separate cogs, SLX rear mech is an acceptable downgrade imo now the arm the cable bolts to is alloy instead of pressed steel, I put nukeproof jockeys on all my rear mechs, I always choose aftermarket chainrings and higher end chains.
Performance, value and a touch of anodised bling works for me, occasionally dabbled with SRAM but never been a fan cos they've broke, I just love Shimano.

I can deffo vouch for the XTR chain being far more durable - I run mine on XT derailleur and SLX shifter with an SLX cassette (12 speed). Zero shifting issues and still going strong after well over 2000km…

I've got a deore 12 speed chain that's 3000km old. Don't they all just last these days?

XTR shifter
XT mech
XT cassette
XT chain

SP41 gear cable inner and outer, everything else is shit in comparison

+ 1 - this is what I have on my bikes - 11 speed and 12 speed.

XTR is more expensive because its lighter weight, not because its more durable. Its a nice bit bling but no functional difference and sod all meaningful weight saving really unless you are a racer.

I think AXS probably worth money on as wireless shifting is supposedly better than cable (not tried it , but others wax lyrical).

If you spend much time in the lower two gears, bear in mind that the alloy rings (one on SLX, two on XT) as well as reducing weight will also wear quicker.

XT shifter as a minimum definitely, for the double upshift (note that's the correct term for changing to a more difficult gear). No experience of the XTR shifter.

Few details of the mechs IIRC. Deore pulley cage is all steel, SLX is half steel half alloy, XT is all alloy. Weight vs. robustness considerations probably. XT jockey wheels gain bearings, there are various opinions on whether this is a pro or a con.

It looks like the deciding factor may well be availability rather than budget.
From looking around it seems that most Shimano groupsets are in very short supply.

I might have to go with a budget build for now using what I’ve got sitting about in the garage then get some nicer bits when they become available again.

personally I'd go as high end as you can afford on the shifter, deore level for the rear mech, then whatever mix of cassette and chain.

Sounds like XTR 12 speed chains are decent from above comments and cassettes I'd pick one based on weight, cost and what freehub body you've got. SLX or XT have always been my go to cassette (albeit not on 12 speed) for cost/weight/performance ratio.