I'm 5'10 and ride a 18" trek. I rode a 16.5" (next size down) just to see what it felt like and it felt like a BMX bike. Which might be good if I rode a lot of technical stuff, but since I ride trails that arn't that technical I like the 18. Even if I did ride technical stuff a lot I don't think I'd have prefered the 16.5" because once I had to pedal up hill or any distance at all I'd hate it.

As far as needing more standover height... I was worried that I wouldn't have enough on the 18" but I've never found myself needing more, or getting racked up *knocks on wood*.

Sometimes it is hard to get going again if I hit a root or rock while pedaling uphill since if I am on the seat in riding position I really have to stretch a foot out on my tippy toes to touch the ground to stay balanced. I still think I have the right sized frame because it's very comfortable to ride.