The pad stack of 649mm from the fit report is correct. The 634mm was just what I figured it would be to the top of the armREST (ignoring the pad), as that was the figure I had to use on the Felt calculator. But anyhoo, the calculator said a 54 frame, and you're saying a 54 from my retul fit report, so sounds promising.
I get what you're saying about the 54 needing less pedestals too - that makes sense.
There aren't any Felt dealers near me, but I'll definitely take your advice when I manage to find one that has a couple of frame sizes I can try out. Just hope the standover height isn't too tall for my short legs! ;)