Can't OC GTX 570 now that it's SLI?

[thepregnantgod]

I have two EVGA GTX 570s. Identical (according to GPU-Z) in hardware ids, etc. I initially could OC my GTX 570 from 732 base clock to upwards of 825 base clock no problem. However, after adding my second GTX 570, any bench prog like 3dMark11, 3dMark Vantage, Heaven bench, etc. hangs my system at any OC.

I'm running these on an Asus P67 Mobo, i5 2500K oc'd to 4.5ghz with 16gigs RAM.

Any ideas what I might be doing wrong?

 

[thepregnantgod]

I'll have to post later today. Looking at the card, I realize the serials don't match the stickers on the card and the box. It was an "opened item" from CompUSA. They assured me it was thoroughly tested and gave me 5% off...but I suspect there's some reason why the wrong $300+ card was returned with the wrong box/wrong sticker. The only way I found out is there's a second serial number - somewhat etched on the card that doesn't match the others.

So I'll get another one and see if I have the same problem.