I always wanted to find a design that uses the slight randomness that particle can have at the exit point of a small pipe, to split them between path that need them both for example. Maybe that could be inspiration for you?
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Ok, I think I'm misremembering things from an early version where that did happen, and I was on the fence about keeping or not. It introduce randomness but that could be cool in this settings. Anyway as a second idea, you can use small turns to change exit depending on velocity, it can probably be a lot smaller than the usual branch.
So basically, I just found a new way to know if a particle is fast enough to pass the branch : when it is fast enough it will go to the upper level. I know that with those exact position of boosts it works but there may be other possibilities. Anyway, I share this because I think this way could help spare some space if well-used
UPDATE : In my session of experiments, I found this shape that basically uses the hitbox of the collision chamber so the particles in the lower loop transform and get into the upper one,just then it transforms again in gravitron + Electron that go through the curve thanks to a glitch (PS, this exact position of the second Collision Chamber and orange Boosts so the particles reach the perfect speed to collide right in the CC