my mobo is the DFI RD600 though, which means i will be unlikely to be able to fit the fan between the top fan and the HSF, thus the push/pull. Also, my HR-05 is really close to the HSF, and will benefit from the air pulled through the HSF.
The other option is to reverse the rear and top fans, and have the Ultra-120 fan pushing up to the top fan, which will extract the hot air. Not sure what that would do seeing that the blower will be firing hot air out the back, which might get sucked back in by the rear fan.
BTW, looks like you have a Noctua on that Ultra-120, do you find it has problems with the restriction of the HSF? I cant feel much air out the other side of my Ultra-120, and was thinking of investing in a fan that resists backpresure better (wide spaced blades of the Noctua have problems with that i think). Not that my temps are BAD, they are pretty good, i just hope i can improve them further, especialy the load ones (52C after 10hrs Orthos, E6400 @ 3.3Ghz 1.425V).