I guess while I'm at it, here are the settings I've found for my Sapphire 7970's that work well with the pool.  The xintensity setting of 4 is exactly -I 13, so no need to change if using that.  It was the thread, gpu engine and powertune that helped on those cards.  Numbers are 736Kh/s at 715wu, putting them very close to a 1:1 Kh/s and wu ratio, which is what you want.  That and keeping your rejects low.   

-g 2
-w 256
--lookup-gap 2
--xintensity 4
--thread-concurrency 16384
--gpu-engine 1055
--gpu-memclock 1500
--gpu-powertune 15
--auto-fan
--temp-target 76
--gpu-vddc 1.170 (for some reason, anything lower causes system crashes, no matter what bios I've tried)