I remember when i was mining with some 280x i have downloaded the wolf-x11Tahitigw64l8ku0.bin for more hashrate. Then i have used this in my config:
"algorithm": "darkcoin-mod",
"device": "all",
"xintensity": "128",
"worksize": "64",
"gpu-engine": "1080",
"gpu-memclock": "1500"...