Hi bigman!

Not such an easy question to answer - Bike companies measure their bikes' "sizes" quite differently. What is a "51cm" in one brand may be as large as a "54cm" in another. Additionally, the frame styles affect fit. Compact geometry frames allow some flexibility; standard frames offer less.

Finally, inseam alone isn't a sure measure. Your foot size and leg geometry matter too. Bowlegged? Your fit is different than for someone who has straight bones. Got monster feet? You may need a larger frame.

In my humble opinion, fit matters. It matters more than anything else about the bike. Unless you've ridden an Ibex in exactly the size you're considering and liked the fit, I wouldn't order from the internet. That's just me, though - if you can afford the potential loss on a bike you don't like (or that doesn't fit), then go for it.

Otherwise, I wouldn't consider spending over $50 on any bike that I can't test ride (extensively) first. I've been-there-and-done-that on a couple of e-Bay purchases that I ended up reselling.

Just my two-cents... Good luck & happy shopping!