I am being told that they can't source a 5750/5770, and that they wouldn't recommend as updates to the drivers are slow to come through. Is this true about updates?
What else would give similar performance at a similar price - up to £120? and run two screens.

Well my GTX275 recently went on eBay for £126 so it might be worth seeing what's on there.

There's plenty of ATi stock at Overclockers though here. I noticed today though that their 5750 prices are only £10-£20 cheaper than the 5770?? The sub-£100 card now seems to be the 5670.

ATi release new catalyst drivers every month (plus occasional hot fixes), whoever said drivers are slow to come through is talking BS.