Impossible to definitively comment on growth rates even after playing with the different settings for the last 10-months or so. I'm confident in saying that chalice growth has been better under the current settings and is hands-down better compared to the growth/color I see (for chalices specifically) under Radium/VHOs. I think it's an awesome fixture for an LPS/zoa tank, which is exactly what I wanted for the ADA 90P it's over. That said, I personally wouldn't put it over an SPS dominated tank. I think the best bet on LPS is a blue T5 set up or setting your LEDs to favor blues. On top of everything about burning corals/growing algae, the 100% White + 100% Blue setting doesn't look good, IMO.
Since you said you wanted to keep a few sps, here are a few corals that I've had really good luck with under the Maxspect: Tyree Setosa (looks the same under halides & LEDs), Yellow Caroliniana (same under both), Green Birdnest (an insane difference in color/growth compared to my halides), Ponope BN, and Miagi Tort. I've tested several SPS under the LEDs, lost some or just moved them back under halides after awhile. We've also tried to acclimate new SPS to the LEDs first and now are trying to bring them back under the halides because the acclimation didn't go well. Part of the fun has been testing things out under different lighting. That's my anecdotal evidence so hope it helps.
