The Roc Plus is a new mold with a slanted rim, the first production model was the R-Pro Roc. I recently obtained both a USGDGC Champ Roc (which is quite firm) and the XG USDGC Roc. Both are great, but I like the XG quite a bit better. It's a tad less stable and really bites when it hits the ground. Perfect for approaches that you don't want to move a lot once they hit the ground close to the basket.
Plus the one I got is a real eye catcher... Day Glo Green with a Rainbow Stamp. Most of them seem to be rainbow stamps. I would highly recommend this disc, I still keep the R-Pro Roc in the bag for understable mid duty if I need it.