I have 370MH/s on 280X and 460MH/s on my 290.
Keccak is epic. Stable as hell, less heat, less power. This has to be the future of coins.
can you please post your config?
280X
core: 1150
mem:750
@echo off
setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS
cgminer.exe --keccak -o stratum+tcp://meth-stratum.hashfever.com:3277 -u worker.x -p x -d 0,1 -I 13,13 -g 1 -w 256 --thread-concurrency 32765
290
core: 1120
mem:630
@echo off
setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
cgminer.exe --keccak -o stratum+tcp://meth-stratum.hashfever.com:3277 -u worker.x -p x -d 2 -I 13 -g 1 -w 256 --thread-concurrency 32765
er ya go

Do you use a cgminer.conf file at all? If you have one and do not realize it then you might have extra options added to your line and not even know it.,