I have £300, and I'm looking to spend this money on a motherboard and cpu. The motherboard needs to support pcie3 so my 7950 will work at full speed.
Your 7950 (or any other current GPU) cannot even fully utilize PCI-e 2.0. The only benefit to 3.0 has been with very high end CFX and SLI configs, how ever the benefit is extremely marginal and nowhere near worth the added cost. For the time being it is my opinion that PCI-e 3.0 is nothing more than a marketing gimmick on high end boards.