I usually use 8# for chucking spinners. A little more water this year, and I had a spool of 10#. So 10# it is.
For backtrolling, my rod (or I sometimes use my buddy's, since it's a 10', which makes it easier to keep the lines apart) is spooled with 30# hi-vis, with 25# leader. I don't have to cast and retrieve while backtrolling. I use that same setup if I'm on the big water (Willy, Columbia).
And to answer your next question -- it's extremely rare I ever break OFF a springer (did snap OFF a winter about a month ago on 8#, which wasn't my first choice, but it was on the reel. But I hooked it out of a drift boat in fast water, and there was nowhere to get the boat slowed down... stuff happens).
I can't imagine going any heavier for tossing hardware in a trib. But to each their own.