Jofa- as far as I know, it will downclock, but not disable shaders. Even so, what I was saying is there are generally more stability issues and stuttering with asymmetrical crossfire. It won't perform slower, and may perform slightly faster, but its not worth is since you are spending an extra $100+ on a 5870 compared to a 5850 for basically the performance of a second 5850, adding in some possible glitches. This comes from doing quite a bit of research into this as I was considering running a 5750 with a 5770 and included a couple of emails with an AMD rep who said performance ought to be just a little faster than 2x5750's.