Performance wise, based upon common game sin Guru3D's test suite, falls right in between the reference $200 560 Ti and the $210 900Mhz 560 Ti.
starting here :
http://www.guru3d.com/article/amd-radeon-hd-7850-and-7870-review/13
COD-MW: 7850 - 127 /
570 - 148
Far Cry 2: 7850 - 78 /
570 - 88
Anno 1404: 7850 - 78 / 570 - 78
3D Mark Vantage P: 7850 - 20710 /
570 - 21931
3D Mark Vantage GPU: 7850 - 19863 /
570 - 21569
Metro 2033: 7850 - 27 /
570 - 28
BFBC2: 7850 - 50 /
570 - 60
3D Mark 11: 7850 - 5521 /
570 - 5584
Crysis 2; 7850 - 42 /
570 - 43
Anno 2070: 7850 - 53 / 570 - 53
BF3: 7850 - 32 /
570 - 37
That's two ties and nine wins for the 570.
Either way, I'd opt for non reference design to maximize overclocking.
Ya can get 25%+ OC's on both the 570 and 7850