case profile and subsequent case stretching

[kbk7478]

what will the difference in case lengthening be for two different cases - for example a 6.5mm-06 a square with 17 degree shoulder vs. a 6.5-06 ackley improved with 40 degree shoulder. Would one see more case stretching on cases with the 17 degree shoulder requiring more case trimming due to that case having not as a sharp angled shoulder? also, can one predict that the ackley case is going to be more efficient on powder burning due to the sharper case shoulder? but looking at load data between these 2 cartridges, the data i have seen shows the 6.5-06 a square developing higher velocities and looking at the 2 cases i would have thought otherwise... any thoughts.