as a sidenote I think some guy mentioned that 2 Brainers on a topic was the most efficient distribution if you're dealing with a bunch of low end topics. Because 50-150% isnt strictly 50, 100, 150.
And due to rounding, for example if you use 1 brainer you pretty much only get 1 unit per day. But if you have 3 brainers its 2-4 (since an exact 4.5 wont come up) so by going from 2 to 3 you've basically only added +1.
4 Brainers is also efficient but if you took those and split them on two topics you force them to give 1-3 units each instead of something fractional. So its more likely if that 4 brainer group would produce "3" units that by working on two projects they may produce 4 units due to rounding.
So generally speaking the only odd-number projects I put brainers on is 1 Brainer studying data discs, gun almanacs, postcards, newspapers, and other fluff.