I have an FOP-32 and made a makeshift shroud for it, then flipped the fan to suck instead of blow. It didn't make much difference, maybe a degree or two warmer at full load. Conversely, I upgrade to the big mutha Swiftech MC-462A and tried the same thing. It definitely did not like being sucked. It uses a 68 cfm fan and the downblast is so strong that is screws up the circulation across the motherboard. Even with a shroud, the temp on the Swiftech went up 5 deg on suck. The good news is, it's such a powerful HSF, that it still works great either way.
Hoot