pcmark vantage black screen

[boldenc]

my system:
EX58-UD3R
i7 920 @ 3.62
HD4770
Antec 1000w
wd 1tb black

system has been tested with intelburntest / furmark / OCCT GPU / 3dmark06 / 3dmark vantage and no problems

my problem is sometimes in the middle of running pcmark vantage tests, my screen turns black or purple, happened 2 times, no BSOD. I noticed that when my HD4770 memory clocks OC'ed, screen keeps flickering, as it switch to default 800MHz when doing video tests and then it goes back to 850MHz, so maybe there is some conficts here? I reverted memory clocks to default 800MHz and no more flickering, I'm currently testing to run 3 runs of pcmark vantage and see how it goes.
anyone experienced this problem? mainly who are using GDDR5 based cards OC'ed

[rebelranger]

I just started getting this.....X58 Classified Dual GTX 275 FTW any ideas as to why

[boldenc]

it was the 4770 causing that, not unstable OC, when the video scene begins, the card switches to stock 850 memory instead of my overclocked settings, and keep switching which cause this back screen for me, running memory @ stock 800 doesn't make this problem. Also happen when I set the memory @ 805 so something is not correct. Try to lower your clocks, also try some OCCT GPU stress test / Furmark to make sure your 275 can handle this clocks

[rebelranger]

I'll do just that... These cards are at stock 712 from EVGA. I have not upped anything on the cards yet but I will do some stress tests.