P5 OS X v.5.0.4.328 is probably stable enough to do 50 characters with 2.5 GB, but remember that P5 is the slowest 3D app for OS X, other than Bryce. All the M2s can be the same, if you just keep reloading them again and again, provided you use Martin C.'s Poser Maconstructor 1.0 in Classic (or DAZ Dial cleaner in X) to delete all unused morphs. Some guy did 34 characters with a G4 and less RAM, maybe 1.5 GB. Just try to run as few concurrent processes as possible.