The only reason to use the PowerColor drivers over the reference ATIs is if Powercolor offers some special features in their drivers not offered by ATI's base drivers. Look hard at the driver features of both (maybe download the ATI equivalent of the drivers that shipped with your card and compare the two. Often the difference is cosmetic (PC logo here and there).
However the ATI drivers should work no problem on your card. The ATI drivers should work on every ATI partner's cards, but it just may not offer you some features (like the Tyan board had thermal sensors long before the rest of the ATI line, and their drivers help monitor that [although you could achieve the same with the reference drivers and rivatuner]).
I would download the ATIs and give them a spin if I were you, the 3.10 drivers have some stability/game/bug fixes in them in addition to the 3.9s. And since you have broadband these downloads/checks should be pretty simple to perfrom.
BTW, glad to see the purchase worked out for you.
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