1)That power supply does not have enough pci connectors for crossfire (although you could use molex to pci)
2)An 8320 will save £30 and will oc to the same ghz as the 8350
3)1600mhz ram will be fine and save you a bit of money
4)the money saved on the components above,will allow you to get a 120gb ssd,so you can put some games on it,as well as the os and some programs
5)a 7950 might be a better choice than 2 7850's as it will run cooler and quieter and use less power and you will still get great frame rates in games on high and ultra settings
6) Personally i would go with the grade b MSI 990XA-GD55 for £70 at ocuk
The build would look something like this:
HIS HD 7950 IceQ BOOST 3072MB GDDR5 PCI-Express Graphics Card (H795QC3G2M) £239.99
AMD Piledriver FX-8 Eight Core 8320 Black Edition 3.50GHz (Socket AM3+) Processor - Retail £119.99
XFX 750W XXX Edition Modular '80 Plus Silver' Power Supply £83.99
Samsung 120GB SSD 840 SATA 6Gb/s Basic - (MZ-7TD120BW) £79.99
**B Grade** MSI 990XA-GD55 AMD 990X Chipset (Socket AM3+) DDR3 Motherboard ** FREE NEXUIZ GAME ** £70.00
BitFenix Shinobi USB3.0 Gaming Windowed Case - Black £59.99
Kingston HyperX Genesis Grey 8GB (2x4GB) DDR3 PC3-12800C9 1600MHz Dual Channel Kit (KHX1600C9D3X2K2/8GX) £49.99
Alpenföhn Matterhorn Pure Edition CPU Cooler (Socket 775 / 1150 / 1155 / 1156 / 1366 / AM2 / AM2+ / AM3 / FM1 / FM2) £29.99
Sub Total :£611.60
Shipping cost assumes delivery to UK Mainland with:
DPD Next Day Parcel
(This can be changed during checkout) Shipping : £12.50
VAT is being charged at 20.00% VAT : £124.82
Total : £748.92