I have heard that the HD 6850 is slightly better than the GTX 460, but not by much. I have an HD 6850 and I am able to play Skyrim and MW3 very well. I would just choose the cheaper option, the GTX 460 is by no means a bad card at all.
They are pretty even in performance and both are a good brand/model. Both should easily overclock the 10% you wish to do. The GTX 460 will be a little quieter than the Cyclone. The only thing that might tempt me towards the Nvidia card is that the most recent 295.79 drivers have greatly improved the performance of Skyrim. My own card (also a GTX 460) saw about a 10-15 FPS increase indoors (caves, ruins) from it. Outdoors also showed about a 5-10 FPS increase. Another plus is that with the improved driver performance I was able to use Ambient Occlusion and still keep good performance. It made the game look really good and isn't available on AMD cards. Still, either card is very good and would do well for you.
I'd get the 6850 because it's newer and performs slightly better on current gen games ( and should perform better on newer releases ). The 400s are old and run hot and loud too
That's just wrong. The HD 6800 series cards came out just a few months after the GTX 460 cards came out in 2010. By your definition I suppose they're both "old". And the reference cooler on the GTX 460 (which I own) is very cool and quiet running - more so than the Cyclone model. The first GTX 460 I had was an MSI Cyclone and I returned it because it was so loud while gaming.
I have an MSI GTX 460 Hawk. I have no problem playing Skyrim on High/Ultra, with the HD Texture pack and following the nvidia tweak guide. Also plays Witcher 2 on High no problems. And it isn't loud at all. My old 8800GT was louder.
The HD 6850 Cyclone Power Edition is an excellent lower midrange card. The O.P. would do fine by choosing it. I just hate to see blatant misinformation about the GTX 460 1GB. I don't know where this myth that the HD 6850 is faster came from, but I see it quoted here all the time. They are pretty much even and more often than not the GTX 460 is faster when there is a difference (stock to stock).