Sorry to report I switched the 6990 rig over to a LTC pool.
Reason : rejects all over the place.
The 7970 rig is still happy moooo-ing away however.
As I mentioned before, the 6990 on I 19 setting does not like the low diff coins.
The 7970's on I 13 dont care about it.
Same mobo/os/miner etc.
It has nothing to do with the pool.
Perhaps I'd better sell the 6990's and buy back 7970 instead....