It will be worth it if you are only planning on using 1 card, although the performance gain is small from a decent 460 1gb. It depends on how much your friend is willing to pay...
I would swap mine for 2x 560ti 448 editions if I knew they would manage better overclocks at lower temps. But i doubt I could get one to 1GHz like my 460, which is why I can play any game on full.