AFAIK, and have seen in game (IL2), Kynetic energy is modelled over distance travelled, but the IL2 damage model works on fairly large 'boxes' that have 'critical' ratings.
In Bob:SOW, there has been mention that the damage model is refined further, possibly where the boxes are a lot smaller... and as mentioned, to calculate all this with a gazillion pieces of hot copper flying around will have an effect on FPS.
