max mpu for 99.8 damage on the pro is 3 mains, 4 subs. i'm still not convinced it's worth it, i've only gotten one 2-shot splat i've noticed. eh.
the pro isn't very ink efficient and i love using splat bombs, so i prefer efficiency on it. 2 subs ink recovery to get my ink back faster (i tend to prefer this to ism overall), 2 subs of sub saver to make throwing splat bombs a little less risky, and 1 sub of sub power up to throw them farther.
the booyah bomb + splat bomb combo can be powerful if used in the right situation (and i've had more success getting kills with it over getting 2-shot kills... but whatever). toss a booyah bomb behind someone then roll a splat bomb in front of them and you're all but guaranteed a splat because there's nowhere for them to run. this isn't the most reliable strategy because it takes ages for the k-pro to get booyah bomb, but if i'm being honest, i'd probably aim more for this over mpu if mpu wasn't the law of the land. (nintendo pls nerf i hate it)