Obviously 750w is a CYA recommendation. For any single 290x to hit the 750w max draw after conversion, you'd have to be sporting a ton of voltage and clocks, probably some dice or ln2 and be using a lightning lol. Thus it's a common denominator baseline, a just in case end of the world number.Anyways, that boot screen looks like a bug perhaps a mb bios compatibilty with gpu bios, ie. option roms in upper memory. Have you updated the mb bios in a while?