Jason: I understand where your coming from. In mod oval our racers that have tested the IB3600 have not seen anymore drop in lap times with the IB compared to the GP cells.
If you own a GFX you can take a few points of the voltage curve and do an average. Example: 5 , 80 , 155 and 230 @ 35 amp discharge or 5, 105, 205 and 305 @ 30.