Hi Dave,
That's a lot of good info and advice there, much appreciated. Great points on the various degrees of slope-age and also the Bike Insight diagrams being inconsistent. I think to clarify: on the current models I definitely would happier riding a current 54cm than a 51. The stack, reach and standover numbers would work better for me, and for the reasons outlined I've raised throughout, I wouldn't be as happy with a 51.
Backstory with the Soma: Went to a lot of time, money and effort to put the project together, importing the frameset and any extra components I needed from outside of Finland (there's not a great amount of, for want of a better word, 'retro' parts here.) Having finished the build, I took it down from the workstand, ready to lower the seatpost on my new 'randonneuse' and to my horror I had to raise it up the way, even further than I'd had it when in the stand. My heart sank when I realised that it looked, to my eyes at least, more like a gravel or mountain bike rather than the one of the machines in BQ I'd been ogling for months and years. I can smile about it now, but at the time it was terrible...
Prior to purchasing I'd been recommended the 52 by 3 out of 4 suppliers I'd contacted. Anyway, standover on the Soma was 765.5mm vs 809mm on my LB. A 51 Sam would be 782mm, a 54, 816mm. Been much much happier with my LB! I think it's fair to say that fit also depends on how the finished bike will be ridden: road, gravel, trails etc... As far as a Sam would go it'd be utilised as a touring rig and would sit nicely in-between my LB and Stooge Rambler. Upthread I've mentioned my misadventures with a Raleigh Competition, last summer's project...
Ofcourse, you're good to point out the dangers of sizing up too big and given that I had to sell on my beautiful Clem for that very reason it's something that I know all too well about. Despite it being a step-thru, Riv's general advice on Clem sizing really didn't work out for me: they're humungous frames! Standover ofcourse was a non-issue but it felt like I had too much bike in front of me, was unwieldy getting it in and out of the house, and I could never somehow find my rhythm on it, unlike my other bikes. So all in all another bike-build-heartache and this time with a substantial financial hit as well...
To summarise then I should probably emphasise again that as Riv's delineation for the Sam's has shifted over the years (there've been 54, 55, 56 and 57...I think?) then, yes, the latest 57 would be too big but that a 51 is not for me. An early Atlantis would be a whole other conversation, no doubt, and getting real for a moment...it's not gonna happen for me here in Europe. Even finding a Sam is going to prove to be quite the task I fear :(
BTW - I hear you about 90s MTBs. Pictured is my Kona Hahanna that's been my daily-driver for 15 years now, used as a commuter, doing the recycling, but mostly as my shopping bike...basically it's my transport, as I'm car-free. Was even my 'road' bike at the beginning :D
All in all, quite the bike really...