If you tell AoC to use more cores it spreads the loads. So on a dual core you'd be around 50-60% total CPU usage and 25-30% total on a quad core. Performance might be very slightly better by spreading the load because you're not overloading a single core but still this is nothing compared to a game that fully uses all the available cores.
I'm talking about physical CPU cores here btw, hyperthreading (virtual cores) is another matter entirely and even modern games rarely make good use of that.