Should I use the HD4000 graphics on my i7 3770k overclocked to the max 1600MHz or something like that or would it be better to go and buy a GPU. And the question is what GPU will i see a performance gain in games, and is there any way I could use both the hd4000 integrated and whatever graphics card i decide on later?
The Intel HD 4000 would basically be comparable to a Radeon HD 5550 which is not even considered a gaming card. The Intel HD 4000 can generally give you decent / good performance using a mix of low and medium graphic settings at 1366x768 resolution for games that are not very graphically demanding. Metro 2033 is an example of a very graphics intensive game that the Intel HD 4000 would not be able to provide decent performance.
Hey there, I just thought I'd let you know what my experience with the HD4000 is. Look below to see my system setup. I play wow with about half of my settings on medium and half on low, no AA and I play at 1080p. In 10 man raids with particle density set to medium i get roughly 30 fps, but in 25 man raids I need to drop all my settings down to low and I still don't get 30. If you can fit it into your budget I'd recommend getting an HD 7850 or better card. The HD4000 will suffice in the short term but it will not satisfy your gaming needs.
The graphics card play no role in video editing unless the program you use specifically uses the graphics card. Otherwise it all depends on the CPU. If the program does not support HyperThreading, then going with the i5-3570k would be the better option. If HT is supported then the i7-3770k can give anywhere between a 10% - 40% improvement depending on how well HT has been implemented into the program's design.