Again though they are using the 15.5 drivers for the 290x and the 15.15 for the 390x.
It seems the new drivert give a 10% to 20% boost in games so it really should be pulling well ahead.
AFAIK the 15.15 has a lot of features disabled compared to the 15.20 drivers.
Actually i'm using the modded 15.200.1040 on W7 64bit, and looking at the dll files it is newer that the 15.15. It gave my 7950 a 3% boost in firestrike tho.