My present DAW is based on an ASUS P6T with i7 920 CPU, RME Multiface, 24GB Ram (still waiting for the new computer parts to arrive). I have an Radeon HD 5750/1GB feeding 3 HD monitors (one of them super-definition).
It all worked fine in Cubase 6 but not good at all in Cubase 7.02: the moment I open the Video window, no matter on what monitor, graphics become very sluggish. Any other window (plugin, transport bar, markers, etc), when dragged across any screen, while the video window is open, had big latency in re-drawing itself. It looked VERY sluggish. Closing the video window would get everything back to normal. The re-drawing issues would not be apparent if an window is static - only when moved. Of course, this would not be a show stopper...but...unfortunately the same issue applied to the cursor as well! Now I had a problem. As soon as the Video window is up, the cursor, too, becomes jerky and this bothered me a lot while working in the editors.
Of course I suspected Cubase to be the culprit and thought I had to wait for yet another update. Until I realized that while there were lots of complains on the Cubase forum, nobody mentioned this one.
So - I installed C7 on an old laptop (with NVidia chipset) - worked perfectly.
I installed the lasted ATI drivers, latest Win updates, latest Quicktime on my DAW - no success. I removed all but one monitor screen and lowered its resolution - to no avail.
I took off an older NVIDIA 8500GT card from my Slave PC, installed it on the DAW - Perfect!!
I borrowed a Zotak Geforce GT640 (NVidia based) from a friend - it worked perfectly with 2 monitors. I couldn't test with the third monitor though because of the stupid mini-HDMI port's location (couldn't plug the hdmi adapter). But again, with Radeon HD5750 I couldn't make it work even with a single monitor.
I am not sure why the present configuration works with C6 but not with C7. Probably the latter uses a different video engine that requires certain instructions set that work better (for me) on a nvidia card.
I don't know...I am probably going to order a Gigabyte Geforce GTX 650 (4 monitors capable) and see how it goes. It is also possible that once I receive the Sabertooth/i7 3939k and build the new DAW I'll realize that Radeon works fine with C7 too...
Thank you all for your input.