Just P6 and P4 (for speed), but multiple runtimes are common no matter what proggie you use (e.g. D|S' directory settings).

I split mine by major figure type - A3, V4, TY2, etc... figures that I know won't have a lot of support I lump together, and I have a separate runtime just for non-human and non-figure-specific stuff (animals, furniture, environments, vehicles, etc).

This way I can load/unload what I need for a specific session... works out pretty good.