Execution order duplication of irules and policies

So in terms of cpu usage, all policies and irules are evaluated and will spend cpu cycles doing so? I know in irules you can disable events to stop the further processing of the same event(s) in other irules, but the policies have a first-match setting. My impression was that the processing of the policies will stop when that first matching condition is hit? So the question still remains if irules are processed first, and then the policies, and if that is correct am I better served with putting the most likely matching condition/policyrule at the top of the policy?