My MSI can handle 5900 Ultra levels. I dont know how because that far exceeds the 2.8 or 2.5ns memory. But i have ran it at that using riva tuner as coolbits keeps screwing around with everything, and it ran fine, except the little tiney fact that i had some image distortion here and there, but hey no worries. I suppose if i got some RAM sinks and found a decent 5900U BIOS i might be able to make it run that high. But for right now i just keep it at 450 800.
-Kevin