I'm 5'10" with a 34" inseam and fit on a 17.5 and a 20" in the trek fx series. Both seem ok - I prefer the 20".

Two things. The new treks will soon be out - the 7500 is known as the 7.5. There's a 7.6 which is between the current 7500 and 7700 in price and features.

I was originally interested in the trek fx but I just kept riding an old 10 speed all summer just to see what kind of riding I would really do and to see if I really wanted to sit upright on a bike. I decided on a cyclocross - wider tires, brakes on the top bar, lighter weight and more positions for riding. But the big thing at this time of year is the price - $200 off of list price. The trek fx bikes sell very well and you probably won't be able to get them on sale.

I wouldn't buy the bike without riding it - just my personal opinion. Although as my brother pointed out to me, any bike I bought would be better than what I'm riding now; and I'd probably like it more - so maybe riding before you buy doesn't matter.