Problem overclocking x1900 Crossifre?

I have an x1900xtx, x1900crossfire with an a8r32mvp. When I use the CCC to overclock my cards my system will freeze during 3dmark06. I have tried pushing it up a little at a time, also tried using the automated overclock utility. My question is I have pcie frequency, peg link mode, pcie voltage and some other settings in my bios, I was hoping that someone has any suggestions on setting for those. Thank you

Currently peg link is disabled, peg buffer length is on auto and pcie voltage is on 1.4, When I had an x1900xtx by itself the card would overclock just fine but now that I am running crossfire that is when all the problems with overclocking have started.

I dont really know how to answer that. I guess that no matter how fast something is people will always want it to be faster. I would assume that any overclock settings that you apply in the ccc would apply to both cards? any yes I am using the stock coolers. I want to get some aftermarket coolers however I need ones that will blow the hot air out the back of the case and not onto the other card, or liquid cooling of course...it does wonders for my cpu temp.