I tested out an RX 480. In order to do so, I had to switch drivers from fglrx 15.something (15.10?) to the new AMDGPU-PRO driver.
122 ms on the 480. D’oh!
On a hunch, I switched back to the R9 290 without switching drivers. 134 ms.
Believe it or not, this is good news. There is a well-documented performance difference between different versions of AMD drivers for OpenCL performance, with the 16.x series usually performing worse, at least for ethereum mining. This performance issue can often be ameliorated even with the new drivers by making a copy of the old version’s OpenCL.dll or libOpenCL.so file, and linking to it at runtime. On Windows, you do that by putting it in the same folder as the mining program. On Linux, you do that with “LD_PRELOAD=/path/to/good/libOpenCL.so ./MyMiningSoftware”. I’ll have to hunt down the desired files and give that a try with the RX 480.
The RX 480 does 10% better than the R9 290 with the AMDGPU-PRO driver and libOpenCL.dll. Perhaps it will still do 10% better with the Catalyst 15 libOpenCL.dll? If so, the RX 480 might get down to 60 ms. I’m curious to find out. Tomorrow, maybe.