Eric,
I'd like to see the low end of the costX sensitivity increased. My sim has population increases of 300% in population sizes due to natural variation (at constant costx). The cycle time of this is in the order of magnitude of 40k cycles. Even at the low end of the scale costx rises too high (2.5) and falls too deep (0,25), resulting in oscillating selection direction, as well as near extinction (only 30 bots left, so I reloaded an autosave).