I'm fairly tall (6'4" or 195cm), and the bike I'm looking for is fairly specialised these days (a tourer, presumably steel, possibly with a sideline as a gravel bike/off-road tourer but no need for full-on CX specs and I need heel clearance). I ride a hybrid. My total road bike miles add up to about the same as a decent ride on my hybrid (42 miles) and those were on a too-small bike. So I'm not familiar with road bike fit. I do know that if I can get the saddle high enough I'll be OK for easily an hour in the saddle of anything.
Nowhere stocks a range of tourers in my size. Even finding one single tourer in stock in my size is rare (tourers don't sell fast).
Of course many places can get one in, try to fit it, fail, send it back, try again... But how do I maximise my chances of getting it right first time? I don't see that a rough fit on a typical road bike or even a CX bike would be very informative, as I'm after the long wheelbase, relaxed geometry of a tourer. It feels like I could extrapolate as well from flat bars. I'd almost be glad if these assumptions were wrong, but I might take a little convincing.
The next step of course is testing it to make sure it fits -- with everything set nominally right it will feel a bit odd as I'm used to flat bars. How can I tell whether this is bad-odd or OK-odd in a short test ride?
Part of my concern is that I'm looking at the Genesis Tour de Fer, and I'm at the top end of the largest size -- by some shops' size guides I should be OK, but not according to others (including the one I may buy it from)