Diamond have managed to pull some serious speed out of the already fast HD 4870; the massive increase in memory clock speeds really manages to give us a serious boost in performance, making it compete against the GTX 280 in a lot of tests.
It doesn't come as any real surprise that the Diamond HD 4870 comes with a bigger price tag, but when looking online the difference seems to be a measly $20. When you look at the performance boost you get, the small increase in price really does seem like nothing.
While the card does manage to use a bit more power, it isn't that much extra and there would be no reason why a power supply that could handle a reference HD 4870 couldn't handle Diamonds XOC Black Edition.
This is one extremely fast card and the small price increase over a stock card makes it an extremely attractive option. If you're looking for the fastest out of the box HD 4870, you can't go past this option from Diamond.