How much do you get with a 280x?
Can you please write your settings?
I'm just getting ~ 40kh/s with the new nfactor. That's quite bad I think.

yacminer --scrypt-chacha -o stratum+tcp://mrcus.nut2pools.com:6000 -u x -p x --buffer-size 2590 -R 7680 --gpu-engine 1150 --gpu-memclock 1500 -g 1 -w 128 --lookup-gap 3 --nfmin 4 --nfmax 30 --starttime 1388361600 --auto-fan --temp-cutoff 90 --temp-overheat 85 --temp-target 60