I agree entirely with Rick. Your employees will always be driven to do what the performance system rewards them for doing, so if you emphasize quick call handling, you'll find (as I did with another client) that call center reps will game the system by answering a customer and then immediately hanging up - thus driving lower average call handling time. Lots of other examples, but perhaps sufficient to demonstrate how clever employees can be to drive the metrics to make them look good.
Many call centers I've worked with put a premium on first call resolution, even if a "warm transfer" to another employee is appropriate. If you ever wonder what are the right customer-focused metrics, don't forget the power of hearing directly from your customers. Sometimes a longer call with resolution is much preferred to a shorter call with a callback required. Even operationally, this should be what your company should desire and drive through your metrics.
Call centers are sophisticated enough nowadays to have a number of metrics available to the casual data observer. The perception is that of a rich variety of available data for decision making, but my clients find that a remarkably small subset of these metrics are sufficient to manage the call center. Thus, don't drown in a sea of data when a few drops will suffice to tell you how well your center is operating.
One final suggestion: a focus on the process of handling a customer's call tends to drive the right results, much more than a focus on the results themselves. You can always mandate better results (and sometimes get them), but it's temporary - take the focus off and results backslide. Focusing instead on the process that drives the results yields more long-term and sustainable improvement.