As far as I know, Techpowerup uses the same drivers for all cards. Their latest GPU review (
980 Ti Matrix from Feb 12th) uses the Radeon Software 16.1 WHQL and shows R9 390 on par with 290X.
In any case, that 290X is 15% more expensive, and that's not even counting the added value of the bundled game. Whatever benches you look at, 290X is nowhere near 15% faster, and even if it was, Sapphire R9 390 would still be money much better spent - Sapphire's cooler is almost certainly much more efficient than the TurboDuo, you get double the VRAM, a backplate, and better resale value due to being newer.