I've yet to see a 7850 not hit 1050 core, which is a 31% overclock. A great overclock by any other standards, that's considered overwhelming for the 7850/7950 which gives you an idea of the average overclocks people are getting.
Meanwhile, the OP gets 1050MHz with more cores for the added cost of getting a pre-OCed 7870, and the non-reference cooler will be nice to have when under load, even not OCed. A bit higher cost, with a bit higher minimum FPS in many games.
HD7850 is better than the 6950 with an overclock but 1GB version is throwing $ away imo. 2GB HD7850, GTX570 for $200 or $190 HD6950 2GB. The minute next generation of games start using > 1GB of VRAM, that 1GB XFX 7850 is worthless unless one doesn't use AA at all.
1GB is a big problem for SKYRIM, 1.28GB still works on the 570.
Agreed, at $200, and I personally think a 448-core 560 with >=2GB RAM would have been perfect. But, 1.25GB is just asking for another RAM-heavy game in the near future, or Skyrim mods out there
now, to create a hard limit by eating up too much VRAM, IMO. As is common, the budget grew, but in games that scale better than Skyrim, the 7870 should offer substantially better min FPS, and IIRC, the OP does have a 120Hz monitor.