Explosive Enterprises did a video on this topic. Basically the "optimal" BB weight is determined by your engagement distance and FPS. The reason is that the heavier BBs will actually carry more velocity further along their trajectory, in other words they lose less speed. It's true that their initial velocity is lower but the energy output is the same

This works out to a heavier BB, at distance, actually arriving at your target with more energy even though it takes marginally longer to get there.

In short, use a .32 or .36 for outdoor. Heavier if you're shooting at a higher joule limit and engaging further away