tl:dl, go with the Roubaix. Long answer- Like many of us, you are overweight. 40 pounds or so? Men carry most of that in our bellies. This makes it harder for us to be comfortable in the drop position. The Roubaix will put you in a more upright, belly friendly position. Either a 56 or 58 would work per the Specialized size chart. You are right in the middle, I think most would prefer the smaller size.