Don't forget immature drivers though...it might turn out to be just as good as the 4870.
I don't think ATI cards suffer from immature drivers, on the contrary, their drivers always push the cards further and further. It's look a lot more like optimization.
Just look at what ATI is doing for the sole purpose of maximazing Crysis results. This game is heavily Nvidia centric, but ATI try to optimize their drivers even if their cards win in many other game less oriented on benchmarks.