I was finally able to pull nearly a solid mh/s from one 290x for over 6 hours stable 
I had instaled Water cooling and after that Cgminer only starts with black screen (no stats)It starting like before - check pools, etc.. but after that only bin file is created and seems that GPU calculated something but - no stats at all.. i cant see HashRate
Sounds weird, but plug the fan in, then remove it. Do this after windows has booted up.
After you've done that, start cgminer. No more black screen.
I am using one of these so I no longer have to plug a fan in.
http://www.frozencpu.com/products/19786/cab-1512/4-Pin_PWM_Male_Fan_Connector_to_4-Pin_Female_Mini_GPU_Fan_Connector_Adapter_Cable.html