Display output off motherboard

[Nuclear Fusion]

Well, basically I wanted to see how well HD 4000 graphics stood up to BF3. So I simply unplugged the DVI cable out of my graphics card, and plugged it into the back of the mobo. I first ran the Cinebench benchmark and got 21FPS, not bad for integrated graphics. In the scores, it recognised it as HD 4000 graphics. I then started up BF3 and set the graphics settings to low (since it is integrated graphics after all). I was pleasantly surprised to find it was perfectly smooth, so I upped the settings to medium. It was still perfectly playable. At this point I was thinking 'Woah, Intel have seriously upped the game with their iGPU'. So then I tried High settings, and it was still fine. I was very suspicious at this point, so I looked at afterburner and unsurprisingly, the GPU usage on my 6850 had been 99%. I was really confused, because although I have Virtu MVP installed, I had it turned off- so I thought that the 6850 wouldn't have any affect on the display output off the motherboard, I thought that only the iGPU would be functioning? Because on the Cinebench test, it recognised it as HD 4000 graphics (hence the 21FPS score), whereas BF3 seemed to still use the 6850- despite using the motherboard DVI output. So I'm confused as to why BF3 was still using the dedicated card when I'd plugged the monitor into the motherboard- not the card, and I had turned off Virtu MVP. Thanks.