I don't believe there is anything magical about Lee's number of six important tasks per day. It could just as easily be five tasks per day. However, I do think there is something magical about imposing limits upon yourself. I find that the single best thing to do when you have too many ideas (or when you're overwhelmed by everything you need to get done) is to prune your ideas and trim away everything that isn't absolutely necessary.
I use a Bullet Journal because of the constraints. It forces a bunch of hard thinking about what is worth writing down and doing.
What constraints do you use?