i use the hdmi converter on one of my DVI outputs as its easier to find a spare longish HDMI cable at my home than DVI, and i think there easier to use. i cant tell the difference between HDMI and DVI but i think theres something there with a VGA (older) computer.
ive got a good old 8800gtx, i havent seen any signs of strain under a 1080p dual screen movie on one side and monitoring on the other. i recon the most blue ray reader would make more of a diffrence, which i consider to be fractional (unless its a complete pile of trash)