if the supernova fits great, why are you looking to replace it?
were you too stretched out on the cannondale?
the geometries of the 51
supernova and the 52
cross concept are essentially identical. they both have 53cm effective toptube lengths. the jamis does has a 5mm longer headtube though, which is insignificant. in my opinion, toptube and headtube lengths are the most important dimensions for fit. they both seem to have the same bb height as well... however, bb height has no affect on fit while riding, only when standing over it.