Measure of performance is different depending on what the goals of the merger are. Relevant KPI’s are determined by the strategy deployed and the synergies being targeted.
For example, in a merger that is focused on creating revenue synergies through expanding a service portfolio, important KPI’s may include top line metrics, as well as retention of key people at the target (those who deliver the desired products). This could be a revenue-vs-goal tracker, and a service weighted retention tracker.
Mergers with different goals will have different effective KPIs.