RD... FIS version. More predictable, easier to ski. Non FIS can work for smaller or lighter skiers, but when we get to 190 lbs or more, FIS ski forebodies just work better as they're a bit stiffer and have a longer turn radius than non-FIS SL's.
Hey Tim, I only figured out now what you meant by RP.... meaning iRace Pro. The iRace Pro is more versatile than a FIS SL and would serve your purposes very well. I've skied both quite a bit, more on the SL, and yes, the SL is more demanding. I think you'd enjoy the iRace Pro or eRace Pro more than the i/e SL RD. Length wise, you can do either the 170 or 175. I ski a 175 specifically because I want more versatility between short and medium radius turns, on and off piste.