I can say from experience that the Nashbar 853 is really nice. I put one together in October and have been riding ever since. I don't know anything about the Rocky Mountain bikes, but they have a great reputation. The Nashbar has a 4130 rear triangle, and as was already mentioned, all or most 853s have this. The ride is very nice, and the weight is within a quarter pound of the more expensive 853 frames. So, while the price is a good deal, I bought it for three reasons. 1) It's a great frame. 2) I don't care about brand names. and 3) Why pay more if you don't see any real advantage. I'm not saying that the other more expensive frames are not better, I just probably would not be able to tell the difference between the RM, the Fisher and the Nashbar. And of course the extra money I saved paid for the new fork I put on Monday....
The picture attached was right after the initial build. I've since put on a nice Marz fork.