If you install the 580 from the beginning, and never boot without it, the iGPU would be automatically disabled anyway. Regardless, there's no performance disadvantage to having it enabled and it HAS to be, in fact, for VirtuMVP to work (if VirtuMVP is able to be used with your mobo).
If you disable IHD4000, it also disables QuickSync, Virtu and maybe something else. QuickSync is for video transcoding (much faster than even GPGPU transcode) while Virtu allows some programs to leverage that particular flavor of heterogeneous computing using the IGP when supported by the software/game.
I have a gigabyte GA-Z77X-UD3H which has VirtuMVP. I dont know exactly what VirtuMVP is. Can you explain?
Am I correct you are saying keep the HD4000 enabled??
VirtuMVP can be used a couple of ways. One is being able to use Quick Sync for video encoding and the other is using the iGPU to get slightly better performance with Vsync enabled (smoother visuals, not extra FPS, obviously, since you're locked into 60 or 120 FPS with Vsync).
And keeping it enabled is completely up to you, I'm just saying that there's no reason you can't leave it enabled (no performance loss).
I use this computer for daily activities, but mostly gaming BF3, Call of Duty Black ops, metro 2033 ect. I like first person multiplayer games, and I hope to start the built tomorrow. I presently connect from my DVI port on graphics card to a 120 3D monitor. I have read differing opinions about enable vs disable. I want the most fps during gaming. Thanks again for the information, but maybe this will help.