I am in the process of buying a new bike I am currently looking at a Cannondale super six. I am 5' 8" with about a 31" inseam I currently ride a Cannondale r1000 caad7 that is 56cm I spoke to a local bike shop and the guy is telling my that that size is way too big for me ?? I feel pretty comfortable on my current bike and have no issues just looking for some input to make sure I am sized properly. Any thoughts? I see charts online and they show I am right where I need to be??