Some help for newbies. Use this miner to get the best hashrate but I think this one is also integrated with the wallet.

https://bitcointalk.org/index.php?topic=652849.0

My results:

R280X -> 12,74 Mh
R290 -> 15,72 Mh

sgminer -k groestlcoin --difficulty-multiplier 0.00390625  -o stratum+tcp://maya.aidbit.net:3032 -u YourWalletAddress -p x -I 22,22,22 -g 1,1,1 --gpu-engine 1200,1200,1100  --gpu-memclock 1050,1050,1000 --gpu-fan 65 -w 256,256,256

Drivers: AMD Catalyst 14.7

I'm pretty sure higher hashrate can be achieved but I was not able to run faster. If anyone is getting better results, feel free to disclose details of your setup.