A spin-transfer torque (STT) switched magnetic tunnel junction (MTJ) enables modern magnetic random access memory (MRAM). Optimization of perpendicularly magnetized MTJ (pMTJ) for MRAM is a comprehensive effort encompassing many materials and device properties characterization techniques, some mature, others novel and innovative. These measurements and characterization methods in combination reveal physical processes of spin-transfer torque switching in a realistic pMTJ, and relationships between materials properties and resulting device performance. An effective set of such metrics made it possible to efficiently optimize STT-switched pMTJ for MRAM. Here we review some of these measurements and metrics, the methodology they brought together, and some lessons learnt in the process.