All the Rockies, Californis and deserts are subspecies of the same species, Ovis canadensis. There is some overlap in horn size, but rockies are bigger on average and upper end in horn size. Deserts have smaller bodies, so a good ram can look like it has even bigger horns...
EF is dead on!
If you look in the record book, there is no comparison. The Rocky minimum to make the B&C book is 180 inches, whereas the Desert variety has a B&C minimum of 168 inches.