I've been pondering what to do with my rig the last few days and come to the conclusion of 'sod it, just upgrade the whole lot' so I am going to do exactly that. 
I'm not sure on a few things so if the kind hardware enthusiasts of OcUK could look over my choices and questions and get back to me I would be most grateful.
I already have monitors (I run the primary at 1920x1080 and secondary at 1920x1200), case, HDDs (including an SSD), keyboard, mouse, Windows 7 etc so none of that stuff. I plan to run it off my current power supply which is a Corsair 650W power supply (I forget the exact model but I can find out when I get home if it's important). I have a Silver Arrow CPU cooler already on the way.
I have so far:
CPU - Intel Core i5-2500K 3.30GHz (Sandybridge) Socket LGA1155 Processor - Retail [BX80623I52500K]
Motherboard - Research on here brings up both the Gigabyte Z68XP-UD3 Intel Z68 and the Asrock Z68 Extreme4 Gen3 Intel Z68 a lot. The Asrock being about £60 more expensive but is it really worth it? What are the differences between the two? I'll probably overclock a bit but nothing extreme no doubt. Any other suggestions even? I only plan to run one graphics card for now (and likely for a long time) but it would be nice to have decent sli features.
Memory - Kingston HyperX Blu 8GB (2x4GB) DDR3 PC3-10666C9 1333MHz Dual Channel Kit (KHX1333C9D3B1K2/8G) [KHX1333C9D3B1K2/8G]
http://www.overclockers.co.uk/showproduct.php?prodid=MY-098-KS&groupid=701&catid=8&subcat=1516
I only selected that memory because it's cheap, but research seems to suggest it's not the best but I'm really not sure what's best for me. Good choice or is there a better one? Again I plan to overclock a bit but nothing too extreme.
Graphics card - Nvidia 560Ti as they seem to be popular at the moment. Not sure which is the best one to get though. Any particular big differences between them all or are they all the same and I should just get the cheapest? Any of them got better coolers than the others (both in terms of volume and temperature reduction)? Any of the companies have better warranties?
Finally anything else I've overlooked?

I'm not sure on a few things so if the kind hardware enthusiasts of OcUK could look over my choices and questions and get back to me I would be most grateful.

I already have monitors (I run the primary at 1920x1080 and secondary at 1920x1200), case, HDDs (including an SSD), keyboard, mouse, Windows 7 etc so none of that stuff. I plan to run it off my current power supply which is a Corsair 650W power supply (I forget the exact model but I can find out when I get home if it's important). I have a Silver Arrow CPU cooler already on the way.
I have so far:
CPU - Intel Core i5-2500K 3.30GHz (Sandybridge) Socket LGA1155 Processor - Retail [BX80623I52500K]
Motherboard - Research on here brings up both the Gigabyte Z68XP-UD3 Intel Z68 and the Asrock Z68 Extreme4 Gen3 Intel Z68 a lot. The Asrock being about £60 more expensive but is it really worth it? What are the differences between the two? I'll probably overclock a bit but nothing extreme no doubt. Any other suggestions even? I only plan to run one graphics card for now (and likely for a long time) but it would be nice to have decent sli features.
Memory - Kingston HyperX Blu 8GB (2x4GB) DDR3 PC3-10666C9 1333MHz Dual Channel Kit (KHX1333C9D3B1K2/8G) [KHX1333C9D3B1K2/8G]
http://www.overclockers.co.uk/showproduct.php?prodid=MY-098-KS&groupid=701&catid=8&subcat=1516
I only selected that memory because it's cheap, but research seems to suggest it's not the best but I'm really not sure what's best for me. Good choice or is there a better one? Again I plan to overclock a bit but nothing too extreme.
Graphics card - Nvidia 560Ti as they seem to be popular at the moment. Not sure which is the best one to get though. Any particular big differences between them all or are they all the same and I should just get the cheapest? Any of them got better coolers than the others (both in terms of volume and temperature reduction)? Any of the companies have better warranties?
Finally anything else I've overlooked?