I have the 05/06 RX8 with a 66mm waist and Fischer (Tyrolia) 12 DIN railflex bindings with the "diagonal heel." I also purchased on Ski Depo a year ago a spare pair of 08/09 RX8 Fires (for less than $300 with bindings). Bindings are the same on the two skis (the newer RX8 Fire may have a slightly upgraded version of the railflex system). Waist is apparently 1mm narrower on the RX8 Fires.
I like my RX8's in moguls, even in icy moguls. I may have difficulties with "stout" moguls, but the skis aren't to blame.
The one thing I don't like about skiing bumps with the RX8's is that in sticky (spring) snow I need to turn the DINs up (from 7 to 8/8.5) or I sometimes manage to twist my boot out of the binding when I plant firmly in a trough and try to pivot the ski. It's pretty clear to me that this is caused by the "diagonal heel." When this happens the ski that I leave behind always stays exactly where I left it, and it takes me about 1/2 a turn to realize that one of my skis is gone. This happened to me once on Catamount Bowl at MRG. A woman who was watching me from the bottom of the slope laughed her head off because it took me far longer than it should have to realize that one of my skis was gone.
I believe the heel on the 10 DIN binding for the RX8 pro is a step down from the "diagonal heel" in the Tyrolia binding lineup. However, I'm not sure that's a bad thing. Only the 12 (and 14) DIN bindings use the diagonal heel. The mojo 15's use the "racing heel" (the name is something like that), which does not include the diagonal release feature.
I like and can recommend the RX8 Fire. I have not skied any of the Progressor series skis, so I can't compare them.