There isn't much info in the forum about this card yet, so I thought I'd share my experience in case someone else can use it.
Stock firmware
At stock I got about 23.5 MH/s with Ethminer and 24.5 MH/s with Claymore (Ethereum only) for each card. All further numbers are Claymore numbers, since that's the better deal, even with the developer fee. Increasing the default 2000 memory clock to 2250 did not improve anything (new frequency confirmed with GPU-Z).
Modded firmware
Atiflash reads a 256 Kb firmware, which flashed without problems for me, despite the warning from Polaris BIOS Editor. I copied the timings of the 1625 strap over everything above that in the firmware, which results in 28 MH/s. I didn't test the 1500 Timings, because someone else here said his card got unstable doing that. Next I tried increasing memory frequency: 2250 resulted in blue screen and 2100 in about 29.7 MH/s, but also in memory errors in the XXX,XXX range, so it seemed better to go back. At stock the cards come with a core frequency of 1288 MHz, which seems high, so I tried lowering it to 1190 MHz. But even that leads to a significant decrease in hashes (~25.5 MH/s). Since power consumption isn't important in my case I just put it back to the default.
After one day
The MH/s seem very stable and there are still zero memory errors. Sometimes the primary GPU drops 1-2 MH/s for a bit, but I guess that's related to it being the primary video card the PC uses.
Stock firmware
At stock I got about 23.5 MH/s with Ethminer and 24.5 MH/s with Claymore (Ethereum only) for each card. All further numbers are Claymore numbers, since that's the better deal, even with the developer fee. Increasing the default 2000 memory clock to 2250 did not improve anything (new frequency confirmed with GPU-Z).
Modded firmware
Atiflash reads a 256 Kb firmware, which flashed without problems for me, despite the warning from Polaris BIOS Editor. I copied the timings of the 1625 strap over everything above that in the firmware, which results in 28 MH/s. I didn't test the 1500 Timings, because someone else here said his card got unstable doing that. Next I tried increasing memory frequency: 2250 resulted in blue screen and 2100 in about 29.7 MH/s, but also in memory errors in the XXX,XXX range, so it seemed better to go back. At stock the cards come with a core frequency of 1288 MHz, which seems high, so I tried lowering it to 1190 MHz. But even that leads to a significant decrease in hashes (~25.5 MH/s). Since power consumption isn't important in my case I just put it back to the default.
After one day
The MH/s seem very stable and there are still zero memory errors. Sometimes the primary GPU drops 1-2 MH/s for a bit, but I guess that's related to it being the primary video card the PC uses.