I haven't had the opportunity to hear the RL-P but I love my Arsenal 12. That being said, I've only heard good things about the RL-P so I really don't think you can go wrong with either of them.
I'm in my mid 40's so I mainly listen to classic rock but I also like some of the younger bands like Collective Soul,Puddle of Mudd,Evanescence,Lacuna Coil,10 Years,etc. I don't listen to rap or hardly anything with synthesized bass but I did listen to "Maria Maria" from Santana's Supernatural release to see what kind of impact the Arsenal 12 was capable of. The entire cabin of my heavily-deadened '98CRV was shaking like crazy and it was giving my kidneys a pretty good pounding.
It replaced an Atlas 12 and the Arsenal exhibits similar SQ, goes quite a bit lower, and it hits MUCH harder. I've found myself turning down my HU's sub output quite a bit so it doesn't overpower the mix. I really liked the Atlas but it's output didn't compare to this thing.