I believe all the suggestions offered up are great KPIs for PMI success. Ultimately it depends on the company what their acquisition goals has been and whether the returns from the investment are met (or at least on track to be met). It is after all an economic decision to acquire, so the economic goals need to be stewarded accordingly with the appropriate KPIs. This does not necessarily mean looking only at hard financial numbers, but holistically at the factors that would affect that assumptions/goals set out in the business case. For example, sales team integration or R&D progress would be just as critical as the immediate bottom line.