You will not be able to overclock the 2500K with an H61 motherboard just so you know. Only a P67 or Z68
Video card wise, you're looking at the AMD 6950 Radeon 2 GB if you can find it for $250, otherwise the Nvidia 560 GTX Ti is right behind it
Is it necessary to Overclock ?
Can't I get enough performance with 2500k and a better graphics card without overclocking?