Woah you sure can run more optimized than that.
We run our 280x @ 725kh/s with 0.5% reject rate
thread-cuncurrency: 8196 (with
Zuikkis kernel)
gpu-thread: 2
intensity: 13
gpu-engine: 1020
gpu-memclock: 1500
Didn't really see an increase in hashrate with Zuikkis kernel but from the look of things my WU seems to have gone up.