I've just installed a 280x (ASUS R9280X-DC2T-3GD5)
Running on Windows 7 with Catalyst 13.12
Using cgminer 3.7.2 with the following options: -I 13 -g 2 -w 256 --thread-concurrency 8192 --shaders 2048
Tried intensity 15 yesterday and had a few HW errors, tried it again today without HW errors but does not increase the hashrate (even tried 20 this morning, computer is mostly unusable and hashrate still around 600)
GPU clock at 1070mhz, GPU memory clock at 6400mhz, temp at 82 celsius
Any idea to increase the hashrate up to 700-800?