9800GX2 plus 8800GT multicard upgrade

I have upgraded my PC's 8800GT to a 9800GX2 powered by a 600W PSU. But as Nvidia now support the multicard option, meaning that it is now possible to put old 8800GT back in the PC. I want to know if my PSU is powerful enough to handle 8800GT along side the 9800GX2.

or should I upgrade the PSU?

This is what I am looking for:-
Card 1: Graphics rendering
Card 2: Dedicated to PhysX acceleration
Graphics card 2 is not required to have the same GPU as graphics card 1
http://www.slizone.com/object/sli_cuda_learn.html

The 9800GX2 to will be the SLI card....and the 8800GT will be the PhysX card.

What I want to know is...is my 600W PSU powerfull enough to handle both cards...or do I have to upgrade...and if so..what is the recommended minimum PSU wattage...

Approx. 200W's is used by CPU & other components...