I just upgraded From Intel Celeron to Intel Core i5-3570K. Def the best. Strong, fast, I can't throw a game at it and make it stutter. Comes out of the box at 3.6GHz (3.8GHz Turbo), by the movement of a slider it went up to 4.7GHz (I paid $20 for a Cooler Master Hyper 212 Evo, fantastic. Look it up).
As for GPU's, I daintily stepped into the GPU realm with a HD Radeon 7770 Vapor-X OC. Cheap and strong as hell. Ignore all this "you need a HD 78xx/79xx to game" hype. I see my card running FC3 ultra. Crysis 3 Very-high. FC3 puts out 97FPS, Crysis 3 68FPS. Guildwars 2 at (get this) high settings 120FPS, 65FPS in world events (over 200 characters rendered at high including effects).
Now. The main reason to get higher than 77xx series AMD cards. The amount of bandwidth increase is INSANE. Including the texel/pixel rate, it might be worth the investment. Increased VRAM (the 1/2/3GB in the name of the card) will be needed in the near future.
I see you're a nvidia guy, but AMD is still viable. I hate to ruin your stability of choice, but take the extra hour to see AMD advantages.