[geoschmo]

My impression from the miniseries was that the Viper VII was faster and more manuverable. So that would explain why they were replacing the Mark II's. Much of the increased performance was computer aided, which turned out to be a huge weakness when the Cylons launched their cyber attack. The surviving Mark VII's on Galactica have been retrofitted to manual controls, which explains why the Mark II's seem to do as well as the Mark VII's in combat now.