The boys did all the testing and posted the results on Facebook, much easier to send everyone there than copy and paste the comments and responses:
Results... Mobil 1 was 6-7k miles old, just prior to being changed out. Coolant, intake air and oil temperature were all monitored and normalized for testing purposes. Test vehicle was a 2013 6.2L with timing dialed back 2-3* from stock to ensure that there were no external factors affecting results.
As expected, Amsoil showed a 1.5% reduction in power output compared to the Mobil 1. Extended wear protection is not without cost somewhere. In our opinion though, an unnoticable 4-5hp difference is worth the longevity achieved with the Amsoil.
For all those interested in lower temperature thermostats as well, this test also proved that higher metal temperatures make more power. On both sets of runs, those with the highest coolant temps (approximately 216* average) made the most power. Those at 190* made the least power. Additional convective heating of cylinder walls = lost cylinder pressure!