I had this issue with my 7950 CF. It would BSOD whenever I ran a game that defaulted to 144hz. There's one temporary fix that I found - disable CF and change the refresh rate to 120hz in the game. Once you do that you can re-enable CF and play normally.
The real fix I found was adding a 2nd CF bridge. However, since you're on a 7990 that would be impossible for you
What was causing the BSOD for me was the pixel clock on the DVI port. ToastyX explains it on this post
I'm not sure how you can fix it with a 7990. You could try this program ( made by Toastyx )
that removes the pixel clock limit but I'd do some research on it in that thread. I haven't used it before so YMMV.
Your friend should notice that if he has the monitor at 144hz in the desktop, his idle clock is higher ( At least for me and a lot of others ). Again, changing to 120hz fixes it. 144hz requires some bit of power to run it properly which is why the memory clocks are raised otherwise you'll get random flickering which I myself still get on the desktop. I just deal with it since I'd rather have lower idle temps than having no flickering Edited by Yvese - 11/3/13 at 7:06am