a new lame-named ATI AIB partner that happens to have the same manufacturer as Inno 3D, has launched its HD4870 card as reported here
The young company posted an interesting performance comparison chart. It claims the HD4870 outperforms the HD4850 and HD3870 X2 by as much as 30 percent in 3Dmark Vantage Extreme tests, scoring X3321 vs. X2573 and X2553. In the Performance test, the situation is a bit different, the HD4870 beats the HD4850 by around 20 percent, scoring P7534 vs. P6235.
When compared to the HD3870 X2 it barely manages to outperform it, scoring just 5 percent more. Basically, the new HD4800 series seems to do a lot better against HD3800 cards in demanding tests with more effects and this makes sense.
You can find the Force3D product page here