I've got similar problem with Gigabyte r9 280x.
I can't in any way get over 300 kH/s. Well it would be nice if it reached something about 350 kH/s ; )
My current settings:
-I 13 --thread-concurrency 8192 -g 1
Any ideas?
And also one thing is bothering me, why I can't set 2 gpu threads (-g 2)?
It's impossible in any configuration : (
I think the gpu threads is probably your problem, but I don't know why you can't set -g 2.
I am running 4 Gigabyte R9 280X cards in one of my rigs on Xubuntu 13.10 and vertminer 0.5.3, gpu BIOS undervolt @ 1.094V. Still tinkering but these settings are what I'm using for now:
--scrypt-vert -I 13 -g 2 -w 256 --thread-concurrency 8192 --gpu-engine=1025 --gpu-memclock=1500 --gpu-powertune=20
http://i57.tinypic.com/29aurg0.jpg