PLEASE HELP! Best budget Editing Graphics card for around £100?

Hi All, 

I'm making a build from scratch and has a small budget of £550 to build am editing rig. 

I will mainly use Sony vegas and CS6 for my editing needs and have left over around £100 for a graphics card. (can push it bit more higher) 

Here is the specs so far ... 

PCPartPicker part list:

Price breakdown by merchant:
CPU: AMD FX-8350 4.0GHz 8-Core Processor  (£117.45 @ Amazon UK) 
Motherboard: Asus M5A97 LE R2.0 ATX AM3+ Motherboard  (£71.77 @ Amazon UK) 
Memory: Kingston Black 16GB (2 x 8GB) DDR3-1600 Memory  (£139.06 @ Amazon UK) 
Storage: Kingston SSDNow V300 Series 240GB 2.5" Solid State Drive  (£71.98 @ Amazon UK) 
Case: NZXT Source 210 (White) ATX Mid Tower Case 
Power Supply: Corsair CX 430W 80+ Bronze Certified Semi-Modular ATX Power Supply  (£35.08 @ Amazon UK) 
Total: £435.34
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-07-29 15:22 BST+0100
I already have an  Windows 8.1 licence. 
Would appreciate any comments and suggestions on this build too.. maybe an Intel system for the same price? 

For your budget probably this XFX Radeon R9 270.


p.s I have limited editing knowledge. You could conversely change it to a similarly priced Gigabyte GTX 660 if you want those CUDA cores.

The 660 from team green or the 270 from team red would be the best choices. Hope this helps :D