Not unthinkable, but the 250W seems a little odd.

When the 8800GTX hit the scene, people were claiming it pulled 225W, since that was the sum of the max wattages of the PCI-E slot+2 PCI-E connectors. They were also claiming that R600 needed 250W, since "apparently" ATI didn't think 2 6-pin connectors were adequate.

Personally, don't care if this thing wants 500W, as long as it uses all that power for performance. Mind, if it DOES use that kind of power, the PSU industry might just cream its collective pants.