I'm assuming you live in the UK, you can get a custom built PC that is both cheaper and higher performance. However, I still think that building your own computer is the best way to go.
http://3xs.scan.co.uk/ShowSystem.asp?SystemID=1513
Configure it as follows
1 *No Custom Colour Required*
1 Gigabyte Z87X-D3H - Intel Z87 Chipset - SLI and CrossfireX support
1 Intel Core i5 4670K, Haswell, 3.4GHz, Quad Core with HT, 6MB Cache
1 Corsair H80 Hydro - High Performance Liquid CPU Cooler
1 8GB (2x4GB) Corsair Vengeance Pro Silver, 1866MHz - Requires Hydro CPU Cooler
1 *No NVIDIA VGA Card Required* (ATI Required)
1 3GB XFX Radeon R9 280X, 850MHz GPU, 2816 Cores, 5000MHz GDDR5
1 600W Corsair Gamer Series PSU, 80PLUS Bronze
1 *Solid State Drive Not Required*
1 1TB Western Digital Blue, SATA 6GB/s, 7200RPM, 64MB Cache
1 *Storage Hard Drive Not Required*
1 Samsung 24x DVD Reader & Writer
1 *DVD Writer Not Required*
1 *Sound Card Not Required Use On Board Sound*
1 *Not Required*
1 *Lighting Effects Not Required*
1 Microsoft Windows 8.1 64-bit - OEM
1 *No Backup Software Required*
1 Microsoft Office 2007 - 60 Day Trial
1 *DVD / Blu Ray Decoding Software Not Required*
1 *No Security Software Required*
1 *No Software Required*
1 *Monitor Not Required*
1 *NVIDIA 3D Vision Not Required*
1 *Gaming Keyboard Not Required*
1 *Gaming Mouse Not Required*
1 *Gaming Mouse Mat Not Required*
1 *Gaming Headphones Not Required*
1 *Speakers Not Required*
1 *Wireless Adaptor Not Required*
1 I have my own network infrastructure!
1 3 Year Warranty - 1st Year Onsite, 2nd & 3rd Year Return to Base (Parts & Labour).
1 Estimated 10 Working Days - Your 3XS system will be built and intensively tested, we aim to have it ready for dispatch within 10 working days.
Total price including VAT is £1,019.99