Good job on your testing! It has been a pleasure to interact with you during the process. I feel you have been very fair and well grounded in reality. The results are about what I expected. The K20 has a higher voltage power supply so I expected it to take the honors on the burst test and it did. The SP2-12000 is not your average amplifier designed for light duty cycles and higher frequencies. It shines at very low and infrasonic frequency performance and high duty cycles. It takes special testing to reveal this performance. My long term sine wave testing is done a single frequency at a time. The initial input level is set to get the maximum undistorted short term power level. Then I graph the output power versus time. This allows you to see how the amp loses power at lower frequencies, how long it holds full power before it cuts back, how smoothly it cuts back (some go into oscillation, some cut off) and what power level it eventually settles at. In your test, the back and forth of which amp is higher may be due to the time constant of the protection circuits interacting with the sweep rate of the test signal as the impedance changed in the load. I don't mean to criticize; it just demonstrates how hard it is to test this stuff.