I would replace cpu, ram, mobo, and gpu. You can keep the same drives, case, and you may need to replace the power supply (depends on how good yours is and the GPU you go with). I had a very very similar system to yours (Q6600, P5k, 8GB ram, 560ti) and went with: I7 3770 (you can get I7 4790 now for the same price) Nvidia…