They are the same performance tier.
Not exactly there - some games would show them together but rezzing up to HD + some juicy AA and watch the 250 topple (not that the 5770 would do that good either)
Nevertheless the justification to upgrade is not there at all. 57XX is only a great upgrade for G94 (9600GT) and below...
I recommend that he go with the Voodoo5 of all things. T-buffer ftw