A very interesting remark. The very same card was unable to speed up more than 1050 for core - when mining Scrypt. After going to Groestl - mem clock was downed to 1000 - the card became much cooler.

And then was easier to speed up the core clock.

Voltage on 12V rail was dropped from 12.7V to 12.02V under Groestl load  - so still within specs.
Under scrypt the voltage dropped to 11.92V - slightly under spec - but still very good.

Now after this new AMD driver - the card became slightly hotter, it is using 25W more - and the hash rate increased for 80%.