It will run them but not very well for a £600 PC due to the very weak graphics card. Its only good for low-medium settings and future games may not run at all at playable frame rates. On a £600 PC you should look for at least a Radeon 7850 on a gaming PC.
The 6770 is still an OK card but on a £600 PC you should get at least a £150 card like a 7850 which his way better. If you can't find one with a 7850 try to get at leat a 6870 or 560 or even better 560Ti or 6950. The guys at toms squeezed a 560 into a $500 PC.
So what? GDDR5 adds at most 15% fps. 36 + 15% = 41. Still only playable on medium on miniature resolution. That video is a joke - I bet it's not ultra settings - look how terrible it looks. Though I am not sure it looks that bad due to settings or due to resolution.