You mentioned that your Aux Copy goes to Tape, however your "Primary copies of these backups where on tape with a multiplexing of 3"?
If the primary concenr is Tape Restore performance, we will need to check the read speed from Tape (should be Clrestore) on the Client and the Write Speed to the Destination (CVD on the MediaAgent).
I would recommend to restore directly to the MediaAgent that has access to the Tape Library and see if the performance is better?
The reason to restore directly to MediaAgent, is so you can bypass the need to write over the network, minimizing the variables.
Hopefully the above helpts