Ok in between all the chatter here ....[lots of stuff] But I would encourage you to see what you can do and try a bunch of different bikes at these places and try to form an opinion that way.
Oh and buy a bike with gears for the road.
as
@stb222 said - i actually did buy a bike with gears! and its a welcome change. i have stopped the SS'ing. because i had to. my body finally gave in. i have some nice hip and knee issues - and my left knee is currently blown up - officially. do i blame SS'ing entirely on this? no way. i have been "overusing" my body (according to science i guess - i call it having fun) since i was a pre-teen. between track (including high and long jump and hurdles), football, bmx bikes, trail running, absurdly long hikes, skiing, rock climbing, mountain biking and road biking, and never stretching besides the times i took up yoga or did PT because things got so bad, my joints have been through the ringer. add my height, and the straw on the camel's back could have been SS'ing, but it wasn't the reason.
anyway - i actually haven't made up my mind - which is definitely rare thing for the board on the "what bike should i get" topic. the FS XXL fat bike thing has crossed the mind. so has a simple bike that maintenance will be a chain and gears (like a rigid fatty)... plus cost, plus a million other things. ask gary - i think it took me three, maybe four years walking into his store asking about road bikes again and again before i finally pulled the trigger.
i wish i could demo a bike, get on it and say "hey this is the one". only time that ever happened was when i demo'd a bike years ago from marty's. a gary fisher sugar i think. other than that, i have always had to buy a bike blind. i'm not made of money, so that kind of spend is a scary proposition - especially at current bike prices. the one i have now worked for years, from 6MR to mountain creek. i don't think any bike is "the" bike, and i try not to think of a "sourlands" bike and a "6MR" bike. i have always only had one ride, and managed to live through it.
anyway - you're right about fitting and bike size... and i have seen the fat bike hate on here, which i find completely absurd. so i figured i would ask in hopes to get something other than the crap on mtbr.