It's not a cheap bike, as you know. So it's wise to demo one for size, at very least in the parking lot, before you buy. No way I can tell what you will like more via internet. I just know I like the large better, and I am running a 40mm stem. It's perfect, the medium had me hovering a bit more over the bars than I like. But the medium would have worked if it was my only option...just glad it wasn't. I am much more comfy on the large which translates to not buying another rig next season. haha right. Then again, height is different depending on if you have a longer torso, shorter legs, or opposite. The standover is not much of a concern between the med and large, so the reach (effective top tube) is more important to evaluate. I have a longer torso/arms so this plays into why I prefer a bit longer cockpit. Make sense? Bottom line is don't guess if you don't have to...find somebody with one in stock and take note of the variables before you pull out the wallet. The bike is absolutely amazing btw...