Well it looks like my current filter is doing fine. The temps are pretty much the same with or without the filter. I even ran some tests twice and got the same results. Apparently my previous testing was flawed. I have also tweaked my GPU OC and fan curves since then, so that may have made the difference also. It is running at 1375 @ 1090mV w/ ram at 1900 @ 900mV. The card was cleaned when I modded the case back in February. Before I started overclocking the GPU it ran warmer, but quieter. Often hitting 85C, but the fans maxed out around 2000rpm. It also hit the power limit and wouldn't hold 1286 constantly. Looks like the only way to lower the GPU temps with the current OC now would be a new heatsink, to expensive, or repaste and maybe install some 120mm fans in place of the current fans / shroud.
Room temp is 24C.
idle filter
GPU max 45C 0rpm
CPU max 36C
System max 35C, max 560rpm
40min game filter
GPU max 81C, max 3648rpm, avg 75C, avg 2813rpm
CPU max 62C
System max 43C, max 1163rpm
40min game no filter
GPU max 80C, max 3384rpm, avg 75C, avg 2925rpm
CPU max 61C
System max 43C, max 1130rpm
Heaven Benchmark filter
GPU max 75C, max 3024rpm
CPU max 50C
System max 40C, max 811rpm
Heaven Benchmark no filter
GPU max 74C, max 3022rpm
CPU max 46C
System max 40C, max 617rpm