Problems getting performance the same across all my rigs?

[mackminer]

I've cgminer running on my rigs with the following command line with linuxcoin.

./cgminer -o **** -O ***** --gpu-engine 900 --gpu-fan 25-80 --gpu-memclock 775 --temp-overheat 85 --intensity 9

There are 3x6990's in each of my 4 rigs, they are MSI cards. With the command line all GPU's in one machine run at 400MH/s within the same temp range of the other cards on the other rigs.

All three other rigs are running 345 average.