I am getting a stable 240 kh/s with your configuration and the same gpu ...
Have you done something else ?
Not anything significant that I can think of. I did crash with intensity 20 after a few hours though, switched to I 19 and so far running stable at 300 kh/s. I have Catalyst 13.9 and I'm on Win7.
I was running on catalyst 13.4. I switched to 13.12 with a thread-currency of 20480 and now I have a decent 300 kh/s.