Well no people here know it as yet except radeon guys. Because it is not yet released.
I'm Not sure if it will be faster then GTX 570, but according to Wikipedia it will cost $300 and I think it will be the same level as 6970/GTX 570 with the power consumption of 6950 or 6870. I think it will be great, but again this is I THINK. Which means it is not real, and we don't know the answer yet . So the conclusion is, if you can wait with your crappy intel HD graphic (I know, it's really annoying and your eyes is hurting of lag ), go wait for a 7870. If no, get a 6950 and make sure you have 2 x 6-pin (or 6+2-pin) and a good quality power supply with at least 30A on the +12V rail to make sure it works .
I wouldn't wish that on anybody , Intel HD is barely good enough for watching HD movies. However noboby knows what the cards will be and how much and what ones will compare with the other side. I doubt that the 7870 will compete with the 570.