I have 5870 and game at same res you are.
Card is fantastic, plays everything well.
Is it, or, is it not good value is completely different matter.
If you are going to play waiting game with hardware releases, well, you can wait for a long time as there is always new card just coming.......
People say that, its never once in the history of the universe been true.
If you listened to only Nvidia sites last November you would have waited a long time if you were waiting for Fermi to launch, but even most of the Nvidia sites cottoned on fairly quickly.
The new cards are releasing in the next couple weeks, the next new cards after that are going to be from Q3 next year into Q2 the year after that if Nvidia has another Fermi like issue on the new process. Theres not a release every few weeks, top end game is changing entirely before xmas, prices, performance, dual gpu, top AMD gpu's, etc, etc.
5870 prices will plummet even lower IF any stock is left after the 6950 is available.
If you have £240 to spend AND want the best, get a 6950, if you just want very good value and very good performance but the best doesn't really matter, a 470GTX is great value(not quite as good as £165 they went for a couple weeks ago

). The only real question is will there still be any good value 470gtx's available by the time the 6970/50 launch in two weeks, probably but they might sell out, the cards are EOL, as are the 480 and 5870/5970.
If you really wanted to buy now, the value is in 5850/6850/6870/470gtx cards and performance is great with all of them.
The 5870/480gtx right now are still not good value, 10% more performance, huge cost increase, the 580gtx is simply terrible value and out of your price range anyway.
Honestly, I'd expect some 470gtx/5850's to still be in stock when the new cards launch, prices will probably improve and there could be some fantastic bargains on them, the 480gtx/5870 could also have better prices, but I can't think of any reason they'd become competitive with 470/5850 pricing.
Today, 470gtx of 5850 and overclock either, they both overclock well, or wait two weeks and get a 6950 which should be around £250, be a pretty decent lead over both(and potentially overclock better) with some very interesting new tech.
If you aren't that fussed about how much it costs, wait, if you prefer value, the 470/5850 likely won't be beaten by any new cards.