You should try some of the Arturia stuff, Bill. Absolutely spot on emulations of most of the great synth classics (Prophet 5, CS-80, Minimoog, Moog Modular, ARP 2600, Jupiter-8 etc.) all done in modeling. These will pretty much bring anything to its knees, especially if you do the same insane layering and stacking that can choke a hardware synth, too.

Bottom line is, it is down to the player.

But unless you install these sorts of things, generally, most arrangers rely on simple sample playback, which taxes a CPU hardly at all. Things like Gigasampler can give you incredibly high voice counts, which might make you think you are invincible! But trust me, start running a bunch of modeled synth stuff. Then start stacking.

Somebody somewhere will ALWAYS find a way to stack too much for any system, then complain that polyphony isn't sufficient. Until there are unlimited resources, this will always be the case..!