I dunno, I can't find a GFX string for it, and almost everyone else I've read who're using the GTX 260 are using GraphicsEnabler and it works perfect. That's what I used before on my old motherboard and it said x16. I ran nvclock and it says I'm "Current Rate: 8X, Maximum Rate: 16X". So, I think it's either my card, or it's some issue with the 10.6.4 drivers like some people have mentioned. I tried using LegacyAGPM and set up an iMac11,1 section with the GTX 260 section from the real AGPM's MacPro4,1 section, and it hasn't made a difference. It actually does seem like the card is running in power save mode all the time. If a launch a game, nvclock still says 300Mhz, when I should be at 626 right? At this point though I've just about hijacked this thread so I guess I ought to start a new one.

Edit: I did just try an EFI string instead of GE, and it still says x8. It's gotta be either my card or my motherboard. Obviously x8 is still plenty of bandwidth for the GTX 260, and everything else is fine, but I don't like that it's not working the way it's supposed to.