Well, think about the widest tires you’ve ridden and ask yourself if you loved the ride? If so, going fatter will likely be even more enjoyable, some people have their limits though.
Also, have you ever thought that the fattest tires you have on a bike were not fat enough to comfortably and safely cross the type of terrain you want to ride? 650b may be for you.
The there are probably lots of other benefits but fitting wider tires four the cushiony ride and hitting the trails is why most people like 650b.
All that being said you have some 26” bikes. I can’t speak to how small large the differences may be there, but I imagine not much.