Okay, I just installed a VF900-CU last night and had the exact opposite conclusion from what the original poster had. My stock load was 80C (variable fan, 665/790 clock), VF900 was 71C, using 3DMark06 as a benchmark. I'm going to pull the VF900 cooler tonight and make sure there is adequate thermal paste in there just to be certain that it can't go any lower.
One note I will make. I am getting multiple VPU Recovers now when attempting to do any automatic overclock, both with ATI Tool and ATI Overdrive, I haven't found the problem yet. It seems to be random, but I can manually set the same overclock as I had with the stock cooler and it is stable. Games are stable, played Day of Defeat: Source for over an hour after the installation with the same settings I had with the stock cooler with no issues.