Can someone explain what the real world difference between these frame geos pls?

Why a Large Holt?

The Burls and Mason are going to feel quite similar in size assuming the stack is similar (not in you figures). Only a few mm different in top tube length and reach. The Mason has a slacker head angle so on steeper doe hills I should be more confidence inspiring. Has slightl shorter chainstays but again not much in it.

The Holt is materially a bigger bike with a longer reach / longer ett (so will feel longer sat down and stood up) - again though we’re missing the stack height. Head angle slacker than your current bike but not as much as the Mason.

why haven’t you compared the large Mason if you’re including the large Holt?

If you like a long dropper post, just keep an eye on how long the seat tubes are.

Size Qs aside, the main difference will be the 2 degree HT angle difference in the 2 bikes. But either way don't buy a new bike now that has the same reach or less as an XC bike from 7 years ago.
You won't feel any differences based on how they're welded, where or by who. Tube dimensions and geometry are the only factors there. Sometimes manipulated tube shapes influence the ride feel, sometimes it's just styling and 'mental FEA' kidology.

But either way don’t buy a new bike now that has the same reach or less as an XC bike from 7 years ago

I'd disagree, if the point of the bike is just pootling about on some bridleways, older XC geometry is absolutely fine. No need for a 64 head angle on a trail someone else is taking a gravel bike down

OP.. be sure the rear axle, seatpost and fork dimensions are the same as what you've got on your current bike if you're planning on just transferring everything over

I’d disagree, if the point of the bike is just pootling about on some bridleways, older XC geometry is absolutely fine. No need for a 64 head angle on a trail someone else is taking a gravel bike down

Sure, I agree and I prefer something shorter than current FS bike trends for a woodland singletrack kind of  HT. But a steeper STA and a front end geometry designed for a shorter stem but all with the same reach as your older bike might not feel great - likely to feel cramped or just odd when adjusted to fit.

Would look at TT length for seated riding also. And why a large Holt when the other 2 are mediums?

I reckon the new Cotic Solaris would be a better bet than either of those. The Holt is too XC - no MTB needs a 67 degree HA and the 27.2mm seatpost is just silly. The Mason is overpriced and not a great looker with the bent seatstays. Both bikes have excessively short chainstays in the larger sizes.

I think it depends on your tolerance for minor changes. I would guess the Raw will feel the most like your current Burls, a bit easier on the descents with the slacker head angle, but you've not included stack height on your spreadsheet so it could be that either are higher/lower which will obvs make a difference how they feel. Also interested in why the Holt is a large?

Here's the frame specs for the Holt in medium.

Thanks all, v helpful.

I think my stack height running a 100mm fork is 605mm.

The reason for large Holt was I'm 180cm tall, and from comments on a previous thread of Holt riders, the advice was in favour of putting me on a large, plus, the reach of the Holt M is less than my current bike, and I kinda like a more stretched position, so don't think I want shorter reach.

So am I right in thinking the head angle is probably the key element making a difference, and a slacker head is better for downhill, but arguably, modest difference elsewhere ... so for me, my riding, probably not a huge difference?

What do you like about your Burls? What do you want to change? 71 to 66 degree head angle change looks the most significant from a steering and handling perspective, slacker will be more stable. Tube diameters might be broadly similar, so rigidity will be unchanged. Weight is a water bottle.

One mans more stable is another mans floppy and slow so worth being sure before going from 71 to 66.

I had a 66 hardtail a few years back (after years of old fashioned XC and even track bikes off road) and while it was absolutely better downhill I didn't like it for general riding and especially not technical uphill

As there is pretty much no downhill where I live I got rid of it!

One mans more stable is another mans floppy and slow so worth being sure before going from 71 to 66.

I had a 66 hardtail a few years back (after years of old fashioned XC and even track bikes off road) and while it was absolutely better downhill I didn’t like it for general riding and especially not technical uphill

I agree.

My Marin is pretty conservative on the geometry front - in fact within a few mm and same head angle as that Holt I notice. It is the lovely balance of nippy enough while stable enough downhill.

I tried a couple of more extreme hartails out - and found the HA and reach were the really defining 'feel' to a bike, along with odd handlebars and different tyre pressures...

I haven’t ridden a bike with a 71 degree HA for a while (unless you count road / gravel bikes). My hardtail is 65 and my full suss is 63.6.

The hardtail feels lovely in most circumstances - it turns and corners quickly, manuals well - and I can’t say the front wanders really.

I’d think 66 degrees is about right for an all round trail ht personally. As long as the chainstays aren’t too short then climbing will be fine.

Aus

The reason for large Holt was I’m 180cm tall, and from comments on a previous thread of Holt riders, the advice was in favour of putting me on a large, plus, the reach of the Holt M is less than my current bike, and I kinda like a more stretched position, so don’t think I want shorter reach.

Just bear in mind that reach is your standing position only - are you looking to be stretched out while seated?