Dual GPUs in old MacPro now possible with Mavericks

Mavericks does allow dual GPU usage. This is software controlled, not hardware.
Application software will have to be dual GPU aware as well. FCPX 10.1 and Motion 5.1 can use both GPUs.
Upgrading to dual GPU's and Mavericks will give the old towers some life yet.
Will be interesting to see speed comparisons between older MP with dual AMD 79XX verses the new MP cylinder. Anyone game?
Here is article by BareFeats showing dual and single GPU in a 2010 MacPro using AMD 7970s
www.barefeats.com/tube02.html

Looks like the improvement is ranging between 24-30% depending on operation.