Take a look at these...
http://www.flickr.com/groups/50-500/
Lots of nice looking stuff in the thumbnails, but many are very soft when viewed a bit larger. Unless you
really need that kind of reach I would stay clear personally.
Having said that I'm a complete 'fast-lens *****' now, having picked my Nikon 80-200 2.8 AF-S up for £500 I could never go back to a slower lens, the quality is just unbelievable. Have you considered the Sigma 70-200mm f/2.8 EX DG MACRO HSM? Reach won't be there but quality will be on a completely different level.
http://www.flickr.com/groups/sigma70-200mm/pool/
Also, £430?! Where is that cheap?