I can get my 280X's to run with settings others have used, but get tons of HW errors. I have 2x Sapphire Dual-X 280X with Elpidia memory.
setx GPU_MAX_ALLOC_PERCENT 200
setx GPU_USE_SYNC_OBJECTS 1
COLOR 0A
vertminer.exe --scrypt-vert -o stratum+tcp://stratum.vertco.in:8080 -u -p -v 1 -w 256 -I 13 -g 2 --lookup-gap 2 --gpu-powertune -20,-20 --temp-overheat 85 --temp-cutoff 90 --gpu-memclock 1500,1500 --gpu-engine 1000,1000 --thread-concurrency 8193