Does 0.2Ghz difference make a big difference?

no you likely wont even see a performance difference for .2Ghz unless you are looking at a bench graph but i think that the i5 line is mostly dual core cpus where as all the i7s are quad or more which will make a big difference under heavy load(when the computer is working hard) if you have the money go for the i7

the 0.2 ghz difference itself will not make a big difference....however, there are major differences between the i5 and the i7....since this is for autocad and gaming, i would suggest the i7 as you will see major differences in performance

the i7 might also suck up a little more power since it is higher power

best of luck

Im running the 15 3570k its the fastest I5 and its great for gaming. Im overclocking it at 4.2 GHz!

I7s have "hyperthreading" which is something that not alot of games incorporate, but is great for rendering and such. It might be useful to you