Appreciate the insights! I chose the Channel Islands (southern limited-load 5-day trip out of Santa Barbara about Truth Aquatic's boat the Vision). Viz. was indeed better (still not Bonaire or Belize good), water expected to be a tad less cold than the northern islands (we hit 1 northern & 3 of the southern), and going the live-aboard route let me cut trip cost way down vs. staying land-based, and avoided those long, tedious boat rides. I was careful about my time of year; definitely seasonally variable, unlike Bonaire (where March, April, December, it doesn't matter all that much).
Richard.