The ex kit isn't available in the US yet, and the Rx is too big for my case. I'd have to mount it to the back, which i don't want to do. But from what I understand I'll be fine with the Rs 360 on an overclocked i7-2600k. my roommate gets 4.6 ghz on a mid level air cooler. So as long as I get a good chip, I'm sure I'll easily get that or higher with much lower temps.
I guess ultimately it depends on what temps you want to achieve compared to what you are getting now. 5ghz isn't really a good option for 24/7 as it requires more voltage than really is safe long-term on those chips. However, if you are happy with where you are now, you should be quite fine with a Rasa kit.
I could have sworn I've seen EX kits available in the US on a couple sites...but I'm not seeing them this morning.