
CPU: You want 2500K instead of 2500, overclocking unlocked and it is dead-easy to overclock 2500K on a Z68 motherboard. Price difference? None. Re-selling value? Way higher.
GPU: 560? You mean 560 Ti? Huge differenc between them. I however would myself and would recommend you too, to buy a 6950 instead. Best price/performance ratio on the market of available graphics cards out at the moment. And you'd be playing all games on the highest settings currently on the stores.

Motherboard: Z68 instead, no real price difference to a P67, but updated features and an ability to use integrated graphics card built-in into the processor. In case your GPU dies some day in the future, so you wouldn't have to wait for a new one in order to use your PC. Plus, using the integrated into rendering (software Lucid Logix VIRTU) is far more powerful than using an external GPU.

PSU: The setup above runs on even a 450W power supply, which we use at work. But as the lower wattage versions on that website are unmarked, I'd go for the 600W Corsair as the last place to save in a PC build is in your power supply.
OS: As for Windows, you can save 70 pounds if you have one on your own already.
Oh and, I know this all because I build custom PC rigs for a living...