How many CP for NPC fodder?

[Dinofreak2000]

yes, a question i figure is regularly asked but my forum-fu is to weak to give friut.

in my next game night the group (hopefully) will make their way into the forest to possibly find out the source of the beasties they hve been hunting.

as such they have made quiet a mess of thier "covert op" with the massacer of guards, tavern customers and the local populace. they have since made themselves known as demon summoners and allround bad guys.

i have decided that causing this much of a ruccaus near the area of their location has alerted the local habitants of the wood.

so i have set up an ambush. it has 4 dark elves (earth/fire mage, archer, spearman, swordsman). the current group have gotten up to 180 cp (and a summoned 300 cp water elemental), so how big should the NPCs be? the 4 are each below 90 cp but close to it. think this is to big? think that having the little encounter here an ambush makes up for the smaller cp totals?

advice is wanted