Bicycle Mechanics - Fitting my frame to my bike frame.

I just purchased a new 2005 Trek 3700 MB but I'm concerned about how it fits me. It's a 21" frame and I'm 6'0. I asked my LBS about it and they said it depended how you want to ride. If I'm going off road then I would want about 3-4" of crotch to frame clearance. If I'm only riding road and hard path trails then fit it like a regular road bike of about 1" clearance. Well I only have about 1" clearance max at this time. I was concerned about rubbing the 3 brake and derailler cables out of adjustment that run on top the frame but the LBS said not to worry about it. Also about quick hop offs, of course. I prefer not to wear a cup when I ride. I don't go off road except for one MB trail and might only do it a couple times a year but I use a different bike for it anyway. I'll be riding mostly paved bike trails and the Katy Trail. I've notice that a lot of MB's have the seat elevated quite a bit but to get my leg length to fit right the seat is not extended but maybe about 4" out of the tube. I'm wanting to pull a BOB trailer eventually with this bike and thought maybe the taller frame might be better for that but it may not make any difference.

Do you think this bike is too big for me and I should go to a 19.5" frame? Is my LBS blowing smoke? The seems to ride ok when I'm in the saddle though. Thanks for any suggestions and comments.

I just purchased a new 2005 Trek 3700 MB but I'm concerned about how it fits me. It's a 21" frame and I'm 6'0. I asked my LBS about it and they said it depended how you want to ride. If I'm going off road then I would want about 3-4" of crotch to frame clearance. If I'm only riding road and hard path trails then fit it like a regular road bike of about 1" clearance. Well I only have about 1" clearance max at this time. I was concerned about rubbing the 3 brake and derailler cables out of adjustment that run on top the frame but the LBS said not to worry about it. Also about quick hop offs, of course. I prefer not to wear a cup when I ride. I don't go off road except for one MB trail and might only do it a couple times a year but I use a different bike for it anyway. I'll be riding mostly paved bike trails and the Katy Trail. I've notice that a lot of MB's have the seat elevated quite a bit but to get my leg length to fit right the seat is not extended but maybe about 4" out of the tube. I'm wanting to pull a BOB trailer eventually with this bike and thought maybe the taller frame might be better for that but it may not make any difference.

Do you think this bike is too big for me and I should go to a 19.5" frame? Is my LBS blowing smoke? The seems to ride ok when I'm in the saddle though. Thanks for any suggestions and comments.It's too big. You also have to consider toptube length which also gets longer with bigger sizes.Try the next size smaller.

Phewy, the frame "size" is many times irrelevant. The big things are the effective top tube and seat height. Get the smallest frame you can get being comfortable on the handle bars (reach) with the seat at the correct height. (e.g. back angle 45, leg slightly flexed with heal on pedal).
I'm ~6 but wear a 31' inseam so I tend to get biger bikes then stores would recomend (21, 22, 58/59 road) because I'd feel cramped (e.g. too upright) on a smaller frame. (it helps that I'm reasonably flexable) However I tend to do heavy XC so I like being a little more streached out as well.
As for standover I've got about 0.5-1' clearance between my sit bones and the top tube (my front rests) and I haven't had a problem with croch checks. The few odd ones I've had were due to poping out of my pedals on a sprint, in which case I'd need like 4' of clearance.
That being said, if you've got a shorter torso then mine I'd check the M 19.5 (or even 18). From the Trek specs for every inch of stand over you gain you'll loose a little less then an inch of reach. If it's a decent shop they should swap the steam out to fit the bike to you. Usually you can fugde a stem enough to go to the next size down.