Not worth it to mine yac with it...I can do 4kh/s but you'd make more money mining something else with 280x cards.

Config:

yacminer --scrypt-chacha -R 4424 -g 1 --buffer-size 2560 --lookup-gap 7 --worksize 256 --gpu-engine 1000 --gpu-memclock 1500 --temp-cutoff 95 --gpu-fan 0-100 --auto-gpu --temp-target 75 --temp-overheat 85 -o stratum+tcp://yac.coinmine.pl:9088 -u ivanlabrie.1 -p x