So I had my 2nd 7970 on the bench putting on a new cooler. Just installed it and the optimizations had no positive effect. With or without the optimization it was only showing about 50% usage. I took out all the optimzation and just installed an app_config.xml using 0.5 cpu and 0.5 gpu (2 wus at a time.) I'm back up to 98 - 99% usage and it completes 2 in 30 minutes or 15 minutes/wu. A figure I can live with.