May as well buy the
OEM CPU rather than the retail version considering you are buying an after-market cooler. Saves a few quid.
Apparently
this is the best thermal paste on the market today.
Do you really need 2000Mhz RAM? You probably could save a few quid and use
this set without noticing any real-world difference. I'm sure I've have heard that there is occasionally problems with getting stable
high overclocks on the i7 when using 2000Mhz RAM, as obviously the internal memory controller is working harder - but I'm not sure.
For PSU I would suggest any of the Corsair HX series. Probably go for the
750W model (higher if you plan to go Crossfire or SLi anytime soon). EDIT: Just noticed that you already have a 750W PSU, just stick with that.
The ATI HD5870 (not sure that this a would fit in your choice of case) or 5850 for the GPU depending on your budget & resolution you game at. Both do well in all modern games - and will probably continue to do so for some time yet. Nvidia still haven't release their DirectX 11 card, it will probably be more powerful but also more expensive. However, if your 280 can handle games then I don't see a need to upgrade just yet - not many DirectX 11 games are on the immediate horizon.
I don't know about sound cards so can't help there.
I would consider dropping the Mobo for a cheaper model, perhaps
this or
this. With the money saved + the money saved on RAM, invest in a
64GB SSD for a boot drive. You will probably get more benefit from this compared to the Mobo & RAM.
Hope this helps
