£650 gaming pc?

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i5-4460 3.2GHz Quad-Core Processor (£130.79 @ Aria PC)
Motherboard: ASRock H97 PRO4 ATX LGA1150 Motherboard (£74.59 @ Overclockers.co.uk)
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-2133 Memory (£57.46 @ Ebuyer)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£39.50 @ Amazon UK)
Video Card: Sapphire Radeon R9 280X 3GB Vapor-X Video Card (£236.75 @ Aria PC)
Case: Corsair 200R ATX Mid Tower Case (£44.99 @ Amazon UK)
Power Supply: XFX 650W 80+ Bronze Certified Semi-Modular ATX Power Supply (£62.69 @ CCL Computers)
Total: £646.77
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-06-02 10:37 BST+0100)


AMD's option:
PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: AMD FX-8320 3.5GHz 8-Core Processor (£105.95 @ Amazon UK)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler (£25.76 @ Amazon UK)
Motherboard: Gigabyte GA-990FXA-UD3 ATX AM3+ Motherboard (£91.00 @ Amazon UK)
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-2133 Memory (£57.46 @ Ebuyer)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£39.50 @ Amazon UK)
Video Card: Gigabyte Radeon R9 280X 3GB WINDFORCE Video Card (£222.99 @ Amazon UK)
Case: Corsair 200R ATX Mid Tower Case (£44.99 @ Amazon UK)
Power Supply: XFX 650W 80+ Bronze Certified Semi-Modular ATX Power Supply (£62.98 @ Amazon UK)
Total: £650.63
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-06-02 10:40 BST+0100)
 
Solution
You can certainly go different ways about this build, a rough outline of what I'd do (no monitor included):

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: AMD FX-8320 3.5GHz 8-Core Processor (£101.99 @ Aria PC)
CPU Cooler: Enermax ETS-T40-TB 86.7 CFM CPU Cooler (£29.74 @ Scan.co.uk)
Motherboard: Gigabyte GA-970A-UD3P ATX AM3+ Motherboard (£63.39 @ Amazon UK)
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-2133 Memory (£57.46 @ Ebuyer)
Storage: Samsung 840 EVO 120GB 2.5" Solid State Drive (£55.85 @ Amazon UK)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£35.94 @ Aria PC)
Video Card: MSI Radeon R9 280X 3GB TWIN FROZR Video Card (£204.34 @ Scan.co.uk)
Case: BitFenix Comrade ATX Mid Tower Case (£28.04 @ Aria PC)
Power Supply: SeaSonic EVO Edition 620W 80+ Bronze Certified Fully-Modular ATX Power Supply (£63.74 @ Scan.co.uk)
Total: £640.49
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-06-02 11:01 BST+0100)
 
AS regard to my previous post on the Intel build: If you are planning to upgrade to a i5 or i7 k model cpu, you can get the Z97 motherboard now so in the future you don't have to change the motherboard.
PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i5-4460 3.2GHz Quad-Core Processor (£134.78 @ Ebuyer)
Motherboard: ASRock Z97 PRO4 ATX LGA1150 Motherboard (£80.08 @ Dabs)
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-2133 Memory (£57.46 @ Ebuyer)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£39.50 @ Amazon UK)
Video Card: Sapphire Radeon R9 280X 3GB Vapor-X Video Card (£236.75 @ Aria PC)
Case: Corsair 200R ATX Mid Tower Case (£44.99 @ Amazon UK)
Power Supply: XFX 650W 80+ Bronze Certified Semi-Modular ATX Power Supply (£62.98 @ Amazon UK)
Total: £656.54
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-06-02 11:03 BST+0100)