With dual gpu's and a cpu block your probably running pretty close to lowest sizes you'd get away with. But unless your heavily overclocked i7 or 8350 and running dual 780ti's or 290's you'll be fine.
I went amd 8350 clocked at 5.2 ghz and 1.54v, which damn near needed a 360 on its own, and then sli 770's. With the corsair 540 air case i put a 360mm, 240mm, and a 140mm in the rear just to play it safe. But i probably couldve done a 240 and 120, but figured my case easily holds the larger, so better safe than sorry.