I thought I'd just mention some rough battery voltage drop tests that I did yesterday. I compared some fairly used Samsung 20S 18560's to a pretty new Samsung 40T 21700. The SXK BB's had the most drop due to the negative battery contact not being the best design/material (I measured between the cell and contact), next was Xvostick with 20S, it was better than theSXK BB's. Then the VA Spade with the 40T, is was by far the least voltage drop. All were firing the some power. All were full charge. BB's dropped to around 3.4, Xvostick to 3.7, VA to 3.95.
45 watt preheat was where voltage drop was made. I never got around to trying newer 20S'.
Edit: all cells rated at 30 amps