The Mac mini shouldn't be considered a Rev. B. The only thing that changed was added RAM for the most part. Everything else has stayed the same.
As far as the hard drive goes it is most likly still the same 4200RPM drive. You might get lucky on the low end and get a 5400RPM drive. Some of the early run 1.25GHz models came with one. I don't know how long that lastest though.