This seems hard to do in my opinion. There are a lot of hard to predict factors, like aerodynamics (riding behind another rider takes much less power) and wind.

This seems hard to do in my opinion. There are a lot of hard to predict factors, like aerodynamics (riding behind another rider takes much less power) and wind. Also the speed and power measurements are usually not extremely precise. There is a few percent of tolerance in most standard equipment. Exact GPS speeds are really hard to measure during cornering or in areas with limited visibility to the sky.