You got four fans on that puppy?
four fans on shrouds in pushpull?
don't switch out for an RX 360, ADD the RX360
to bluntly answer the question though, the RS240 is the 'weak' link, its a thin rad and you obviously want more power :P
No shrouds, but I have two CM Blade Masters pushing and the two fans that came with the kit pulling.
And adding the rad is a viable option, since I can still mount the RS240 at the bottom of my Phantom. But, would the pump be able to handle adding a 360 rad?