If you want to mine Groestlcoin,  use ccminer v0.3 release

https://github.com/cbuchner1/ccminer/releases/tag/v0.3

This one does 20 MHash/s on 3 ASUS MARS ROG cards on Linux.
That's six GTX 760 cores by the way. I solo'ed 4 blocks within 8 hours.

Unfortunately we were a little late this time and phm has published
an AMD miner much earlier (2 hours after coin release)

nVidia may be looking quite OK compared to AMD this time.

Christian