Hi Derry I have tested with viewer 3 and firestorm. They both work equally well with the driver setup i posted however, i have a very beefy system so its hard to notice much difference.
In general tho i believe firestorm/phoenix always seemed to do more on the gpu side. I think since firestorm uses a huge amount of base code from viewer 3 its not the case so much.
HTH
Drager