I have an XT45x420 in the top with fans mounted above and a UT60x 280 mounted in the bottom at the moment, both pushing air into the case. All fans are blowing into the case so as to use the cooler air from outside the case rather than the warm air from inside the case to cool the rads.
Plan was I would add the "pull" fans when Phanteks started selling the additional PCBs. But now that I have it running .... I don't see the need.
Running every stress test I can thro at it.... and after just dropping teh fan speeds way down .... I can't get the water over 34C (was 31C with fan speeds at 1000 rpm) ..... CPU is at 4.6 GHz, typically topping out at 75C under RoG Real Bench and under Furmark, GFX card temps are like 40C after 30 minutes... my pump rpm under PWM is about 50% - 65% ....rad fans are at 750 - 850 rpm ... I have both case sides open and can't hear a thing with front fans less than 15 inches from my left ear. Ambient is 21.8C .... so I'm seeing a delta T of 10C at 1000 rpm and and 13C at 750ish
So that should answer ya push / only question ....
As for fit ....I went with the XT45 cause I thought it would be too close to call....I posted some pics many many pages back of the wider UT60-280 / XT45-420 in place....sure I can dig up again. It wud have fit in push / pull but just by 2 mm or so with the M6F.....dunno about your board.....but the M6F has a huge heatsink ..... look at Jesse's pics also (he put in both 140 and 120mm wides so ya can compare) .....access to ya 8 pin EPS cable may be an issue
the right side of the fan under that rad would miss the heat sink by about 2mm
Just bumped up fan speed to 1100 and here's what I am seeing....
Pump => UT60x280 Rad In (31.4C) => Rad Out (30.4C) => 780s in SLI Parallel Loop WBs => XT45 Rad In (32.7C) => Rad Out (31.6C) => CPU WB => Res => Pump
I can hear the fans tho....GFX (32% OC = 1175 Core / 1227 Boost / 7524 mem) at 39C and CPU (4.6 Ghz) at 38C ....
EDIT: While I was typing this was playing with fan speeds.... setting it up to give me 10C (out of 2nd rad) under Furmark at about 940 rpm it looks like... Ambient = 21.3 last rad out = 31.3 ..... 39C on GFX and CPUEdited by JackNaylorPE - 11/28/13 at 7:43pm