Using an r9 280x, I'm getting around 8631 kh/s . I have to say that although the gpu usage is 99% it doesn't seems to stress the gpu as much as dogecoin mining for example. The card stays at a cool 62c using a fan speed of 42% (Sapphire).
Dogecoin is scrypt based which uses a good bit more resources than these hash algorithms.
Scrypt is about as intense you can get while still being able to run on a GPU.
Sadly the performance does drop to 100 after 30mins. Any one else have that issue?