Sanotal :
What are you trying to say? I'm telling him that he will see a performance increase if he were to get the parts that were talked about. When did I say "You can only have this because your old motherboard etc" I'm literally just saying "This is better than this"
Oh, the way it was worded, it sounded like you were saying that because he already had a Core2Quad and a GTX 260 that it was better to use Intel and nVidia. Believe it or not, I've heard crazier things from people. If that was not what you meant, I apologise.
Now to the OP:
You wanted it kept under £400-£500 so we'll do that. Generally, I've found that EclipseUK is the best source for computer components in the UK so I will use them. If you can find better prices on the same gear, by all means, go for it.
CPU: AMD FX-6300 (6-core, 3.5GHz) - £89.94 inc. VAT
http://www.eclipsecomputers.com/product.aspx?code=CPA-FX6300
Motherboard: ASRock 990FX Extreme4 - £120.60 inc.VAT
http://www.eclipsecomputers.com/product.aspx?code=MBA-990FX4
Video Card: AMD R9 280X (HD 7970) 3GB - £227.10 inc.VAT
http://www.eclipsecomputers.com/product.aspx?code=GC-XR928X2
Total: £437.70 inc. VAT
That neatly fits into your budget and will make your computer an amazing gaming machine. I checked and the RAM used on the EVGA nForce 790i SLI FTW motherboard you already have is DDR3 so just transfer your RAM to the new motherboard. You'll be quite happy with the results as the R9-280X is the same card as the HD 7970 (that I have two of) and the GTX 260 just cannot compare to it. I know, I had two Radeon HD 4870s in crossfire (the HD 4870 and the GTX 260 ran about equal back in the day) for four years but one R9-280X is more powerful than even those two meaning that you will more than double your gaming performance with this setup. Before getting the motherboard and CPU however, I would recommend getting the card and seeing how it works with your existing setup. If it is satisfactory to you, I would just go with that. Your motherboard is made for gaming and I don't think that the Core2Quad will be a huge bottleneck to this card. It will be one, but if you get the results you want, despite the bottleneck, that is all that really matters isn't it? Cheers!