With my settings every card under I=14 is usable
If you have an iGpu maybe consider that as an option too?
EDIT:
In the cgminer readme it says the default intensity is 'd' for desktop interactive performance. Try setting the intensity of the card you use for your monitor to 'd'.
dunno about you, but when scrypt with d my hashrate drops to 10-25% while at 13 desktop is usable and mining at least 80%