Unless you plan on lowering the bike or you have long legs for your height, you'll probably have to lower said bike to be somewhat comfortable. I'm 5'9-10" with kinda short legs and it took me a while to get comfortable on my stock GSXR. I ended up lowering it to realize that should've been my first move. Find something comfortable, but don't be scared to lower it if it makes it better. With that said, I've had a few 12 second cars and have ridden a few dirtbikes and quads, but the older 600 still surprised the shit out of me with how quick it is. If you have some brains, sense, and coordination don't be scared to start on a 600 or bigger.