Of course..the HD5670 is an entry/budget level card; the GTX460 is a performance-end card. There's a huge difference between them in price, power, and power-consumption. That's like comparing an HD4850 to a GTX280, or, for the lovely car analogies, an SUV to a Porsche.
On the other hand, if he can go to an e-tailor, I'd get this card.
One of the best overclockers and it's only $45 more.
Alternatively you could wait for the ATI's newer cards that are coming out relatively soon.