£610 gaming pc including windows 7

PCPartPicker part list / Price breakdown by merchant

CPU: AMD FX-6300 3.5GHz 6-Core Processor (£74.20 @ Amazon UK)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler (£23.82 @ CCL Computers)
Motherboard: Gigabyte GA-970A-UD3P ATX AM3+ Motherboard (£65.87 @ Aria PC)
Memory: Mushkin Stealth 8GB (2 x 4GB) DDR3-1600 Memory (£59.94 @ Aria PC)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£39.99 @ Amazon UK)
Video Card: XFX Radeon R9 280 3GB Black Edition Double Dissipation Video Card (£162.58 @ CCL Computers)
Case: Fractal Design Core 2300 ATX Full Tower Case (£37.99 @ Novatech)
Power Supply: Silverstone Strider Essential 600W 80+ Bronze Certified ATX Power Supply (£50.04 @ Scan.co.uk)
Optical Drive: Lite-On iHAS124-14 DVD/CD Writer (£10.79 @ Amazon UK)
Operating System: Microsoft Windows 8 (OEM) (64-bit) (£75.35 @ Ebuyer)
Total: £600.57
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-11-17 02:05 GMT+0000

you could use win 7 64 bit but its not a great idea .
Win 8 has a better license that lets you reuse it on another computer . 7 oem is locked to the first motherboard
And its simple to add a start button to win 8 using Classic Shell .Once you have done that it behaves like 7 anyway
 
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