I have a few old parts and I am thinking to put together a new system for Internet browsing, office applications and movies watching. I have a z77 motherboard, 8GB DDR3 and an i3-2120. I could also buy a secondhand i5-2500k or even an i7-2600k. I don't plan to overclock and I am wondering if the difference in performance will be noticeable compared to the i3-2120 that I already have. What do you think?