FWIW, you're not running a 2 saw plan. You just have an old saw as a backup for your 261, which is perfectly fine (an definitely not a bad idea). For what you're cutting, if you go to a 2 saw plan, I think the 400 or 500 would be fantastic depending on what you need for a long bar and how heavy of a power head you're willing to carry around. Either way, for the bigger saw I'd have at least 2 bars. One for big stuff when you need it, and another shorter bar in the 18" to 20" range that will rip through your firewood like lighting
If you're sometimes doing 50 cord a year, IMHO, that's enough work to keep a 261 and a 500 plenty busy.
As far as the video goes, I think it was largely a waste of time. It showed that bigger saws cut faster so long as they aren't wearing a bar that's 4x longer than the wood actually needs.