I'm using Prolimatech Megahalems, with 2 Scythe SlipStream 1600/1200RPM push/pull with good results. It is keeping my hot w3520 cool&quiet up to 4.3HZ 1.28v.

I have tried a to replace the 1600RPM with a 38mm Scythe Ultra Kaze 2000RPM but i it didn't make much difference on temp. It seams to be performing optimal with "normal funs", but Scythe Ultra Kaze was too noisy and maybe i didn't try hard enough.