Well i discovered that the recently purchased Trek for $120 is 16.5 inches (FRAME) and im 5 Feet 9" inches tall. There is a clearance of roughly 3" from crotch. Is this size bike salvageable for my height with perhaps a slightly longer seat post?

it doesn't sound too bad- a lot of people run mountain bikes with a good bit of post, me included.

I'm 5'6 and ride a 15" frame. You need that crotch clearance- unless you want to sing soprano.

Just get a longer seat stem

The fit depends more on your riding style and your desired reach (i.e., effective top tube length and stem length) rather than the seat tube length.

too small .. at least for my taste it would be.. I'd get an 17 or 18

Well with a slightly longer 1" post my leg extension is almost complete so at 16.75 the frame isnt terribly small from what i can see. Thanks for your input folks.

3" is to close for comfort, 1 went from a tall trek 8500(old outdated peice of %#@) that was about a 16.5 to 17" tall and alot of clearence problems seeing is as how i'm only 5'6" so when i got my fsr i dropped down to a medium to a 14.5-15" height and the ride is alot better and more comfortable.

Glad you got your rigs issue solved happy riding

I'm 5'6" w/ 32" inseam and love my 15.5" mongoose. However, there have been a couple of occasions out on the trails where I found the knee-to-stem dimension a little tight for my tastes.

I'm rolling my 17" KHS on the trails from here on out.

A 16.5 doesn't sound that bad for you...