You haven't seen the scads of post stating not put 5xxx/6xxx cards in the same rig as 7xxx? Which I believe is stated in the FAQ as well?
Wow. I don't see it in the FAQ, but I wish I had seen the posts before I invested in the 7850.
Thank you for the pointer.
If you use 2.6 you can get the same performance than 2.4/2.5 with 5xxx cards only if you compile the phatk kernel (for cgminer this is done automatically on the first run) on a 2.4 or 2.5 based system.
You'll have to move the resulting bin file on the 2.6+ based system and force cgminer to use it (the -k option overrides its default choice for the kernel).
I still have one Xubuntu 11.04 system configured in case cgminer tunes its OpenCL kernels again and I have to recompile them.
Thanks, this is really helpful. I'll experiment with this before I start thinking about getting rid of my 6850.