I have a system with multiple video cards which are supported GPUs. Will this accelerate my Catalyst workflow?

Applications covered by this FAQ: Catalyst Prepare (ver. 3.0 or later), Catalyst Browse, Catalyst Prepare (versions previous to 3.0), Catalyst Edit

The short answer is, unfortunately, no. For Catalyst, installing more graphics cards will not accelerate further Catalyst workflows. It may slow you down due to slower CPU-GPU data transfers as the PCI Express bus will be shared and the PCIEX16 slot will operate at up to x8 mode.