I read that longer than 300cm is only really worthwhile for organised rescues/probe lines?
that sounds ridiculous.
it really depends on your snowpack where you are riding. continental snow never gets as deep as coastal stuff so the slides won't be as deep. its a personal decision. for me i'd easily rather carry a slightly longer, beefier and consequently heavier probe because in the event i have to ever use it it will be during a class 11 shitstorm and i'd much rather err on the side of being prepared.
these are tools to save a life. not worth it for me to use the bare minimum.