The 6870 is a supremely powerful card for it's buck. Scoring at 17 points per dollar on the GPU Benchmarking tests it's the most cost effective way to get up to a 3k score. It compares right there with the Nvidia 560 GTX Ti's, only 100 points in difference from it.
That card is the one I intend to buy, and it has 2GB of onboard memory, superiorly important how much of a difference this makes, people with 580 GTX's for example and 1GB of onboard memory have frame rate issues while their GPU Load isn't at max because their Virtual Memory is sitting at full load. Trust me man, that 2GB vs 1GB is such a massive difference in the GPU area.