With an i7 you shouldn't have much problem.

I would think that the alt-tab problem would be caused from the video card if you reinstalled the software.
I would start by reinstalling the driver in device manager. If that fails you could try switching out your card for another if you have one.

My best guesses. GL!

I have another card in my other computer. Its a Geforce GTX 650 Ti I think.
Do I need to install different drivers after changing them? (I want to change them just to see if it's like you said any problems with my video card)

tabbing in game doesnt cause much problems, tabbing in menu screen is worse

Yeah, you gota update your drivers if you change video cards.

Alright, going to try this tomorrow. Thanks

run in windows mode, update drivers, reinstall direct x 11

you have to use windowed fullscreen or it flickers really bad for the stream

First reaction to random shit happening on a beast computer is "I should update my drivers". Always.

I had this same exact problem awhile back.

I stream occasionally too, so it would crash in mid-game and I would lose ladder points.

Try:

~ Repair SC2. (should be on one of the tabs on the Launcher under Help or something).
~ Run in Window Mode. (I had trouble with Full-Screen mode, kept crashing mid-game).
~ Close out of Skype. (Skype can be a common problem for preformance).

If you need anymore help, feel free to PM me.