RS240 or EX240 for temp case

I'm going to be taking the water cooling out of my AMD rig and I'll be doing some more modding of my Rosewill Challenger case - in the mean time, the intel machine will go into a Rosewill Patriot case. The patriot can only handle a 240 rad inside (I want to use it inside the case for temp housing) so, with the D5 vario pump do I use the EX or RS rad (I have both) on a Swiftech Apogee XT block cooling a 2500k only
For some reason I'm thinking the EX240 is more efficient although it is a thinner rad (radiator frame is the same size) I haven't looked at the fin count on each since the RS is still mounted in P/P