Need some more details. Are you interested in saving money? Seems like you already have a i7 930 and a motherboard for it which you say you can use to overlock your cpu in which case, it could be a more than capable cpu for gaming. What gpu are you currently using? Do you have the i3 right now as well or would you need to buy it along with a motherboard?
Personally, I think the 930 is not bad and having 4 real cores is a benefit. I would not consider it an upgrade to go from 4 real cores with hyperthreading to 2 cores with hyperthreading. Although the haswell i3 would be faster in day to day tasks, for gaming, especially now with DX12 and stuff, you'd want to keep the cores. I would put my money elsewhere but it all depends on your situation. If you really want a cpu upgrade, I think you should aim higher.