If you want to throw in an i7 CPU, go ahead. It is ultimately your build.
Just don't expect a performance difference in the usage your after. The i7's Hyperthreading on really helps in multi-threaded applications like most video-editing, 3D modelling and compute programs.
Thanks for the advice on that one. With the build you gave would you reccomend an SLI setup or just stick with the one video card. I'm looking to invest in a good PC that will last me a few years or so before I have to upgrade anything on it. I mean, the lady PC I bought was an Alienware about 5 years ago *ducks*
The build I made above can handle another card in Crossfire (SLI is for Nvidia cards) but I didn't include it as I don't know your monitor setup.
Its not worth adding more cards until you get a high resolution monitor, something like an Eyefinity setup or a 120hz.
A 7970 will get you 50+ FPS at Ultra in games at 1080p, adding in another card will only give you a 10FPS increase (if that) because you will then be limited by V-sync. So you need a display solution that can actually take advantage of all the graphics horsepower.