Here are the figures that may help you.....
FPSC stock media (scifi and ww2 characters): polycount ranges from 1000 through 2200 and vertices from 1200 through 6400.
Official Model Packs 1 & 4: polycount ranges from 1400 through 1800 and vertices around 4400-4600.
Murkymedia's actor pack: polycount around 2222 and vertices around 6600. Even though this may be the highest of all 3, it is actually the smoothest running character pack. Somehow these models have been designed to work very well with FPSC, much better then all the other ones around.
I've made an animated model once which had a polycount of 7200 and 3900 vertices and it still worked fine, even when putting up to 8 in one level, the player could see all 8 of them at once. But, it had a special written not to demanding script attached to it and that makes a difference also. Try doing that with the stock characters and you'll soon be having a game that won't run to well.
It's the combination of polycount/vertices and the script that influence the outcome. Often scripts added to control the characters, are way more demanding then the models themselve.