I have ridden both extensively. The Racing Ralph definitely gets the edge as far as rolling resistance goes. The Rocket Ron is definitely a fast tire for how open and tall the tread blocks are. The only thing I didn't like about the RoRo is the knobs seemed a little flexy until worn down a little as a front tire. The RaRa's tread blocks are shorter and closer together. The RoRo also gets an edge in ride quality with the nicer casing.
Quite honestly I think having a set of RaRa's around and a set of RoRo's would be perfect. For dry fast conditions RaRa's all the way. When things get a little slick or gnarlier, RoRo. And by gnarly I mean a rougher XC course. The Schwalbe tires are still fairly puncture prone down the tread section whether you have the Snakeskin version or not. The Snakeskin version only has a heavier duty sidewall.
That being said I didn't puncture my RoRo's once last season. Since upgrading to the Tubeless Ready beads for this season, I bet these tires are even nicer than they were before. Mine always setup tubeless on Stan's rims well. On my old Edge/Enve wheels they took a little more work, but once sealed were good for the season. Also, tread wear-wise, my RoRo's lasted all year (April-October) and are now being ridden by another friend.