Hmmm...I'm almost an inch taller than you with a .5" longer inseam and my Cannondale is a 48 (though that would be comparable to a 50 in just about every other brand...TT is 51.5, IIRC). I would not want anything even the tiniest bit larger. I sometimes wish my TT were maybe a cm shorter, to be honest. I started with an 80mm stem, but steering was pretty squirrely. Went up to 100mm, but that was too much. 90 is a decent compromise, but I'm still pretty stretched-out and my girl bits pay some for that.