I have both the GTX 670 and ATI 5870 in my Mac Pro. Under iStat menus it only ever shows the 5870 (which is in PCI slot 1). It shows the card's VRAM as maxed out, for some reason. Every once in awhile when I boot the computer it shows the GTX 670 and not even a quarter of its VRAM is being used. But 99% of the time it is the 5870 that is shown in the iStat menus. I am not running any applications when it shows this. The system is completely idle. Is this something I should worry about? Do you think it is just iStat menus messing up because of the dual GPU's, and with one being a Windows cards? Thanks.