Thousands of polymers have been synthesized to produce membranes for gas permeation. Currently, their potential as a viable material is often bench-marked in the so-called Robeson plot. This plot gives a first impression of the transport properties at ideal low pressure conditions and ambient temperature. However, these data are of limited significance as they do not represent realistic process conditions. Here, we present a new methodology which allows a more comprehensive judgment of membrane transport properties based on their influence on overall processing costs. In particular, we apply this methodology to the question whether the materials discovered so far offer benefits when applied at sub-ambient temperatures. For a variety of applications, this rigorous approach proves that for certain materials the overall process costs can be minimized by applying sub-ambient process conditions. It also emphasizes that temperature-dependent permeation data is important to be reported for new materials.