Here. Better cpu, motherboard, RAM, and added a power supply.
PCPartPicker part list:
http://uk.pcpartpicker.com/p/32Rql
Price breakdown by merchant: http://uk.pcpartpicker.com/p/32Rql/by_merchant/
Benchmarks: http://uk.pcpartpicker.com/p/32Rql/benchmarks/
CPU: Intel Core i5-4570 3.2GHz Quad-Core Processor (£139.19 @ Aria PC)
Motherboard: Gigabyte GA-B85M-D2V Micro ATX LGA1150 Motherboard (£43.02 @ Scan.co.uk)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory (£64.99 @ Amazon UK)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£43.54 @ Amazon UK)
Video Card: Gigabyte GeForce GTX 780 3GB Video Card (£399.30 @ Amazon UK)
Case: Cooler Master N200 MicroATX Mid Tower Case (£33.83 @ Aria PC)
Power Supply: EVGA 600B 600W 80+ Bronze Certified ATX Power Supply (£48.78 @ Scan.co.uk)
Monitor: Asus VE247H 23.6" Monitor (£119.99 @ Amazon UK)
Keyboard: Gigabyte GK-FORCE K7 Wired Gaming Keyboard (£34.92 @ CCL Computers)
Mouse: Gigabyte GM-M8000X Wired Laser Mouse (£41.99 @ Amazon UK)
Headphones: Corsair Vengeance 1300 5.1 Channel Headset (£29.99 @ Ebuyer)
Total: £999.54
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-03-02 18:56 GMT+0000)