Eventually coral wars will occur and a decision needs to made. I kept the corals that I liked the most. Speed of growth was not a factor. I only keep fish and corals that excite me. I loosely defined Bonsai by the amount of rock used. For example, a 100g tank with 25 - 50 lbs of rock with artistic elements could be described as such.
A mixed system can work, the challenge is balancing the correct nutrient and light requirements to keep everything thriving. I often hear, "Why is this coral doing so well, but the SPS are dying?", and vice versa.
Stick to bullet-proof SPS and you can focus on the zoa's as they are the primary actors.