Productivity metrics for development team

We have been thinking of some number based targets for our development team. The idea is to show productivity gains to the client over a period of time. Though there needs to be a lot of thought and brain hacking which has to done before we come up with these kinds of metrics, at present, only 2 metrics come to my mind right away.

We can have a quality metric which can be something like an average no of SIT defects attributed to code/design per total number of SIT test cases. Since we have already collected these data over the past 2 years, over many projects executed under the program, we have some idea of this figure and what we can target to achieve in the future. 

The other obvious metrics which can be given as a target is the defect turnaround time. This figure also is available for the past data and we can give a target value for the development leads for this metrics. But when I think hard, this metric is not fool proof. For example, we can track the total defect closure time from the time a defect was opened till it was finally closed. But the time spent in the various state of the defect in between those 2 end states are not tracked. And who should be responsible for it.  If the development team fixes a defect but testing team just sits on it and whiles away time before retesting it, it will look bad on the development team numbers.

Another fact is that both these metrics are lag indicator of the project quality. Neither is a lead indicator. Ideally, I would like to have some lead indicators which can be used to take preventive/ in course corrective actions.