56 is a smaller bike fir a guy as big as you. I'm on a smaller bike and im 6'2 33-34" in seam and ride a 60.
Its all about you fit on each bike. Manufacture, torso, inseam, seat post, seat position, handle bar stem, all that plays in.
1st into a bike shop and have them fit you on a bike. try different bike manufactures regardless of price and then try common manufactured. look for bikes in that size range. If you then find a bike of a private seller, take the bike in to a shop and have it fitted and inspected before you pull the trigger.
Forget carbon fiber, expensive group sets and nice wheels...if you dont fit on your bike properly...you aint got shit.