OK, just had a quick play after extracting everything Nvidia out of the iMac update (including AppleGPUPowerManagement) and it doesn't appear to have made a difference. I think the drivers I got from Nvidia fixed the mess that 10.6.4 made but they are apparently specific to the GTX 285.
I was playing WoW prior to the update and sadly I can't run it on high or extreme but still get decent detail but FPS drop to ~30 in Dalaran.
I applied those kexts via Pacifist, touched the Extensions folder and restarted and yeah, no different. I also checked the driver version and it says version 2.1 Nvidia 1.6.18. Sadly I don't know what it was prior as I didn't know where to find it at the time.
I have noticed a bit of screen tearing though, this is only when I'm not using any graphics intensive apps. Weird thing is, It doesn't appear when a game is running like if I have WoW in windowed mode and quickly move a window around, it's smooth but if WoW is closed (or any other game) I get the tearing. This was happening before I played around with the drivers.
Would be awesome if I can get Ultra settings in WoW with a constant 60fps
Also, if anyone's wondering. Here's the contents of the driver from Nvidia (19.5.8f03.dmg).
It appears as though that will work with most Nvidia cards although their site said it was specific to GTX 285.