H80 so yeh 120mm Rad. Couldn't fit a 240mm in without hacking the case to bits so best i could do really
external rad? a idea perhaps tbh i found that the perform worse than air, has it got stock fans?
could try push pull with say typhoons or sp 120's but i doubt it would make a huge difference
also i posted here way back at beginning that placement of rad helps a lot, is yours on exhaust as all the hot air gets pulled through rad adding to the heat.
if you have top fan and your cooler on rear try having cooler blow in and top fan exhaust least rad gets cold air that way.
you will get sluightly negative pressure causing tad more dust but may help temps, so to recap
have front,rear, side, and bottom as intake top as exhaust as heat rise anyways. cool air coming through rad is a must, ifound exhaust on rad gave increase of temps