If I plug the DVI to my single monitor to play games there and plug HDMI to my HDTV to watch movies, will I lose fps performance if I do both at the same time? (Playing bf3 in my single 1080p monitor while my family is watching movie on the HDTV?) Thanks
It's gonna be really hard to run and control those at the same time, and yes it will affect performance if you manage to do it. But you're gonna have a lot of things to sort out like how to control both at the same time and how to reroute the audio etc. I don't think it's worth the hassle.
I do this already while my wife is watching series on a 1080p 42" Sony while I'm playing games on 1080p 23" Samsung. I tell you it works but FPS significantly drops like ~30-40%. Plus not all applications and games support choosing audio output device. you may end up having the sound from only the TV or the Monitor/Speaker/Headphone etc..
edit: probably you'll experience better performance than me since you are on SLI.