Slow video rendering etc. in FCP/Premiere/etc. Radeon problem with Mountain Lion?

My mid 2010 Mac Pro was working fine until I installed Mountain Lion. My colleague has the exact same setup as I do, but has SnowLeopard and no issues. Mountain Lion may or may not be the problem.

Now, all video takes a really long time to render or encode or export, especially .mov. Testing on FCP, Premiere, Compressor, and Media Encoder, Quicktime 7, results in really long times for anything involving video processing.

All other video works fine; playback capture, etc. Just processing of video takes a really long time.

I thought it might be an issue with the video card?

Mid 2010 Mac Pro

2x2.66 GHz 6-Core Intel Xeon

12 GB 1333 MHz DDR3 ECC

ATI Radeon HD 5770 1024 MB

OSX 10.8.2

I may have to resort to a clean install of Snow Leopard and just go back to when things worked...