The only real performance difference is that aluminum heads are lighter. It's really a toss-up of which is better...loosing weight or loosing heat in the cylinder.
Ideal, you want as much as a cold intake charge as you can get going into the cylinder...stuff as much air in there as possible. However, once the intake valve closes...if you could create as much heat and compression as possible...and keep it all in the cylinder you would see some pretty wild cylinder pressure.
Think of it this way...if you throw an aerosol can on the ground..it does nothing
, but if you throw it in a fire...it takes off
Murdock