filter plant is my go-to solo run at high water. i stop running bridges solo around 3 feet or so.
everyone looks for different things in their boating. soloing has given me some of the best experiences i've ever had on the river. it's all what you make of it.
the whole "never go alone" attitude is absurd and way too generalized. stay well within your comfort level, of course. but solo 50 days in a season and you'll be rethinking the whole soloing taboo.
and yes, it's great at 4feet. moving fast, but still pretty forgiving.
even better at 5feet