I'm using 4 120mm Noctua fans that aren't in pushpull. I don't think I could fit pushpull on top without cutting out the top of the case which I'm not sure I want to do at this point. At stock my CPU idles at about 40c but under load it can hit 60 so I think I'm over the 15c delta you're talking...
Ok so first I figured I'd post my system:
i7 3770K @ Stock (ATM) w/Koolance 370
ASUS Maximus Formula V
16GB DDR3 2133
EVGA GTX690 w/Koolance 690 block.
2x Vertex 4 256s in raid
EssenceSTX
My cooling loop currently is as follows:
PMP450 on a RP-452X2 1.2 --> RX360 --> 370 --> RX120 --> GTX690...