how much better than a 8800gts?

the question really is what type of setup do you have?

Do u have any single problem with your 8800GTS 640? is there a game that u can't play @ good settings?
HD 4870 is better than 8800GTS 640 but if u dont have any problems with your setup then don't change it because its something new.

MACER1; C2D 6600@ 2.4 GHz, gigabyte 965 sp (rev 3), 2 Gb OCZ ddr2 800, 250 Gb hdd, Hyper 850 Watt psu 24" 1920x1200 tft, all standard settings as I`m holding up any overclocking until it is really needed!
MAZIAR; No no problems with any game until AA is activated in which case there can be a big drop in frames in some, something that seems to affect the 4870 much less than the 8800. I was mainly curious to see if anyone had yet done this upgrade, if so what improvements were noticed, particularly with AA enabled.
And, sage advice in your last paragraph! I`ll keep my money in my pocket for now!

Ive got a GTS320Mb, and as soon as theres a certain 4870 out, Im jumping on it. Im tired of not having maxxed out gaming. Little slow downs etc. Plus I should be set up for any newer games. Id say its close to 50% better, or so, maybe more. The 4850 is better than the Ultra and the 9800GTX, and the 4870 is about 25% better than the 4850, if that helps

If u have a SLI board, why not SLI it? 2 8800GTS 640 will outperform many current cards.

also jaydee, doesn't HD 4850 have an edge over a 9800GTX? (i mean in most games the HD 4850 leads but not by much and in some other games the 9800GTX leads but again not by much)

At higher res and more filters it wins out in the close ones, plus the ones it already wins. I agree, if the OP has sli, then go for that. Also, thats why the GTX dropped in price, to make it competitive, thats why its lower priced, and the GTX+ is coming to compete edge it out, tho, all you need to do is oc the 4850. Plus, as these are new cards, driver potential is much higher than on older tech, so I believe in the end, the 4850 will prove to be stronger than the GTX+ as well

Oh i see,yeah in higher resolutions with AA and AF the HD 4850 shines.
thankf for the info  

Just put my full spec on my sig, sorry, I`m a noob at this forum lark!

@MAZIAR: My mb is 1x 16x pcie1  

The aim of my question is to see if anyone has made the same or similar upgrade and what the results were, particularly
at higher resolutions with filters enabled.
Yes I am looking to upgrade in the near future but... Would a 4870 offer a big enough jump in MINIMUM frame rates
at 1920x1200 with AA enabled to justify the cost? Is it £180 better under these conditions? I have so far resisted other upgrades due to prohibitive cost, silly power requirments or just lack of performance improvement, and now that the X2 cards are rapidly becoming obsolete from a upgrade point of view the way forward seems (fairly) clear. Or is it?

Yes for 1920x1200 with AA, a HD 4870 would be a good boost for u