I'm fairly sure most people would reccommend the RX over the RS, basically, if you can afford it, then go for it, there's no reason not to, after all it will give you more headroom for future upgrades too.
^+1, I'm a bit of an Xspc addict and I'm afraid to say that when they released the EX series, they pretty much shot the Rs out of the game,
I will never recommend them because the Ex is the same size (if size in your case is an issue) and performs almost as good as the RX (twice the thickness and costs more)
if you have room, RX, if not EX
I just bought two EX360's for an addition to my rig, and for the money I'm over the moon, but I currently cool an Amd 975 at 4.5GHz, idle is 41'c
thats only when I'm playing though, I'm at 4GHz normally