I am trying to find more info on the transmission ring limit and the queue limit on the asa. Seems TAC is suggesting that the QUEUE and Tx ring limit stay at their default values and every model auto sets its limits at boot up time. The defaults always seem to be 256 = Tx rin and 2048 for the Queue however. Is is this across the board on all ASAs. Can I assume the Tx ring limit is the # of packets that indicate WHEN congestion occur and the Priority Queue enforced? Lastly, why not change both values to the highest possible setting? that seems to give the most BW to the Priority Queue.
I would suggest reading http://www.cisco.com/en/US/docs/security/asa/asa80/configuration/guide/qos.html#wp1083195 that explains how to calculate these values and what they are.
Setting the queue limit to the maximum value would save you from tail drops but it also depends on how much memory you have available.
As for the tx ring, that is the maximum number of "normal-not high priority" packets that can be put in the transmit queue before we tell the interface queue to buffer until the congestion clears. In other words you would like that number to be low so that not many normal packets are transmitted while we are congested. The you would kill your normal packets apps though. so there is a trade off.
I hope it makes sense.