I have seen some big jumps (20-25%) in performance from drivers in certain games, and 10-15% overall on occasions. But not often, and not for a very long time.
Some of the results people are posting are raising a lot of unanswered questions, and I think we are seeing a lot of BS being thrown about TBH.
That is often true of same architectures, theres a reason the 480gtx gained almost smeg all from launch to now, look at even the biased TPU results, the 480gtx is almost identical in games from launch to now with only 1-2 noticeable increases.
A new architecture leaves HUGE room for improvement, but as said, the numbers just don't really add up at all so far, we'll have to see.
Basically he can be using drivers that, well the drivers support dx11, the card can translate dx11 instructions, but that doesn't mean the driver is in any way optimised for that architecture.
The numbers are ALL over the place, and that suggest drivers that just aren't optimised.
Has he said where he got the drivers from, a disc or is he just using the latest from AMD's site?
Anyway, as I hinted at, if he did get it from a friend(or if he works at powercolor himself) and not at retail, you'd lie about it to cover your friend. So we can't really say for sure where he got it, if its a shipping model, if Powercolor have the right bios/drivers, anything really.