gigabyte r9 280x 61.45kh/s
on Win7, Cata 13.12
with cgminer.exe --neoscrypt -I 14 --worksize 48 -g 1 ....
2x Gigabyte Radeon R9 280X 3GB GDDR5 (Windforce x3) OC GURU II
2x Sapphire Radeon R9 280X 3GB GDDR5 Vapor-X
same here but.....76kh/s : cgminer.exe --neoscrypt -I 13 --worksize 24 -g 1
in cgminer.conf change : "intensity" : "13", "worksize" : "24", and add : "gpu-fan" : "0-80",
all other change that fit your need.
Good Luck