Hehe, blooming university students - can trust any of em
That XFX card is a great choice, and the warranty is rather nice. However, if you are able to wait I would suggest looking for the
ASUS version as it uses "Voltage Tweak Technology". It sounds a bit silly, but it allows you to easily overclock your graphics card and keep it within the 3 year ASUS warranty, rather nice deal IMHO.
As for factory overclocked cards, all the cards I see available on OCUK seem to be running at the same speed - so there isn't an option for factory overclocked cards yet. The 5850 is fast enough already, but if a factory overclocked version turns up, I would wait for a review and see if the extra performance is worth the (inevitable) higher asking price.