Abstract : This report is a continuation of our previous research effort on statistical program performance analysis and comparison, in presence of program performance variability. In the previous study, we gave a formal statistical methodology to analyse program speedups based on mean or median performance metrics: execution time, energy consumption, etc. However mean or median observed performances do not always reflect the user's feeling of performance, especially when the performances are really instable. In the current study, we propose additional precise performance metrics, based on performance modelling using gaussian mixtures. We explore the difference between parametric and non parametric statistics applied on program performance analysis. Our additional statistical metrics for analysing and comparing program performances give the user more precise decision tools to select best code versions, not necessarily based on mean or median numbers. Also, we provide a new metric to estimate performance variability based on gaussian mixture model. Our statistical methods are implemented with R and distributed as open source code.