FYI, R9 290 (non-X), AMD 14.4, new settings yield 3800 KH/s:
-I 19 --gpu-engine 1000 --gpu-memclock 1500 -g 2 -w 128 --thread-concurrency 20481
Only if you are lucky enough to be able to get 1500 memclock. If you have crap Elpida memory that won't OC above 1400mhz like me, just use stock mem clock and I 18 for 3700KH/s (and probably less power usage).