With all due respect to Tom's best card for the money features, which are a great starting point, you have to look at the realities of pricing, especially post-rebate. Tom's doesn't include rebates and is pretty conservative in telling you what the price of a card is. But there is no doubt that the 560 or the 6850 is a faster card than the 7770, even if it's not as efficient. In fact, you can even tell that from the article--the 6850 is recommended at ~$150. It wouldn't be recommended at a higher price than the 7770 unless it offered more.
Also see, e.g., these benchmarks:
http://www.anandtech.com/bench/Product/536?vs=539
It's true that the 7770 probably has a bit more to offer from driver updates than the 6850 does at the end of its realistic driver update cycle. But that isn't going to close the 20-30% gap (or more) with the 6850 or the 560.
The 7770 is only appropriate, IMO, in very low-power situations. Your 460W PSU does not put you in that category. Get the 560 or 6850.
edit: all this, of course, is contingent on your willingness to tolerate rebates. If you can't float the $15-30, then of course the 7770 is still a fine card, and definitely better than a 6770 or 550 Ti.