AMD Unveils R9 285 Graphics Powerhouse, Shipping Next Week
It's also worth noting that AMD is no longer pimping the Radeon R9 280, and while the Sunnyvale chip designer didn't come right out and say it, reading between the lines seems to reveal that the Radeon R9 285 is intended to be a replacement, with speculation that it's based on AMD's new Tonga GPU.
Getting right down to the nitty-gritty, the Radeon R9 285 brings with it 1,792 stream processors, 112 texture units, 32 ROPs, 918MHz boost clockspeed (core clock is unknown at this time), 2GB of GDDR5 memory clocked at 5.5GHz on a 256-bit bus, and a 190W typical power rating. Compared to the Radeon R9 280, it's very similar, except the 280 has a faster boost clockspeed (933MHz), a wider memory bus (384-bit), and a slower memory clockspeed (5GHz).
Though AMD doesn't advertise different Graphics Core Next (GCN) versions, it seems likely the Radeon R9 285 is rocking version 1.1, which would give it some performance optimizations over the Radeon R9 280. What we know for sure is that the card supports DirectX 12, Mantle, and TrueAudio technology.

Perhaps the best part of all this is pricing. AMD says the Radeon R9 285 will be available on September 2 for $249, which is $50 less expensive than the Radeon R9 280X.