Theoretically hydros should be just as fast in reverse, but whether [I'm guessing for safety] HydroGear designs them that way or the mower mfg does, reverse is ussually around 1/2 to 2/3 of forward.
I've never seen CC say explicitly either speed on the RZT, but plenty of the the other EZT users are around the 4-4.5 reverse and 6.5-7.5 forward speeds. Also note that the Z-Force is at 4 and 7 with IZTs (EZT's "big brother"). Really though, if you can do those speeds [especially on the areas the RZT was designed for] you'll be fine.
After looking over many mowers and many specs, I will be the first to say the ZF is a better unit in the CC line; but if you have about an acre of fairly smooth ground, you'll likely be very satisfied with a RZT50. Confused yet?! /forums/images/graemlins/crazy.gif /forums/images/graemlins/grin.gif