Project Manager Metrics

What metrics do you use to determine whether your project managers are productive? Things I have considered include: Managing to budget, delivering on time (projetc and milestones), issues resolved, size of team managed, number of milestones managed, number of faeturs managed, size of budget, and so on.

What I really need is a way to determine who has a bigger/smaller workload and who is using their time more productivly than others from a purely PM view. This is not how shoudla PM manage development productivity.

Thanks.