Please try mining groestl directly at groestlcoin.biz. It is 0% fee.
One R9 290 there should give you approximately 600 GRS per day. See stats here: http://groestlcoin.biz/workers (counting R9 290 = 25 MHS)
On this pool, one R9 290 will give you about 750 GRS.

PS: Diff decreased because some miners did not move from cryptohunger.com when I disconnected it recently.

Thanks