So I have a AMD Phenom II x4 945 and GTX 285 OC, I have some cash, and want to do some upgrading, I have a few different routes I can take, I can either get a AMD Phenom II x6 1090T, and get a case(i hate my antec 900), I can also just buy a Gtx 560 Ti and not upgrade my CPU, or I can or I can get a i5 2500k which is only 179.99 at microcenter which is only 5 minutes away from me at my current place im staying the weekend at in cincy, but if i get the 2500k, I will have to sell my 945 and mobo, and cpu cooler, and buy a nice motherboard/cpu cooler to put the 2500k in..Opinions guys/gals? All will be appreciated

Just wanna know what I should do, and which would give me the biggest boost in performance, ive been dreaming of a 2500k build xD