With HT off, I'm getting around 65% GPU load with my 480 and full CPU thread, and around 8 minutes for a WU.
With HT on, sharing CPU cycle with 12 threads of WGC, I'm getting around 60% GPU load, and 9 minutes for a WU.

My 480 is overclocked to 850Mhz though, so that's got to contribute to reduce the work time.

Getting a steady stream of WUs from GPUGRID at the moment, with pauses of around 10 minute max before receiving a new WU to crunch.