2xGTX470 would cost a lot more than 2 GTX460 and he can OC the GTX460's to reach 2xGTX470 level. (aka HD5970 level LOL:D)
Not that much, a GTX460 1GB costs ~$240, in which the GTX470s would cots only $120 more.
You can also OC the GTX470s too, to GTX480 SLI level. XD