The optimal environment for LiPo batteries depends on what you do with them.

• Optimal performance: 50 °C to 60 °C. This also means that this is the temperature at which the cell Internal Resistance (IR) is the lowest.
• Storage temperature: 10 °C to 20 °C. At 10 °C or below, do not charge the cells at more than 4.1V/Cell

The problem now is - as we can't heat up the cells to 50 °C for our testings - to find the coefficient to apply to the temperature at the moment of measuring the cells.

Quote found on the internet of someone having spent quite some time with this topic:
My personal internal resistance number for high performance cells is 12000 / cell capacity, when measured after stabilization at room temp (~21C) for 1 hour minimum.. Anything around or below this number I consider to be outstanding performance.

See the attached Graph for an idea on what influence temperatures have. Also - this graph was taken from the following thread

This is what the Computation will be based on, after applying the correction factor for the temperature.

The discussion can be found here

A very good article around RC LiPo can be found here: Understanding RC LiPo Batteries