I don't know your rig, but IMO, definitely wide-angle, assuming you have a good strobe or two. Most of the ops do the deepest dives first thing in the morning, and it can get darkish down those slopes. But big schools of fish, potential pelagic fly-by encounters (especially @ Shark Shoal dive), and neat topography (Pilot's rock, Diamond Rock, Outer Limits, etc) with a lot of growth would point more to wide angle for me. Some of those (Diamond Rock in particular) make good 2nd and 3rd dives maxing around 70' depth, and in the sun they can be amazingly colorful. So still wide angle in my opinion.
You can expect vis anywhere from 100' down to 35-40' depending on the dive site (the shallower sites can be a bit poorer, weather dependent, especially if you're lucky enough to dive Green Island off the northern shore, which can be sandy but pretty cool). I haven't been there for years but I think we had one dive around 40' vis, but mostly 70' or above, and we were there roughly this time of year (although I see you're not going until August).
Are you staying longer in St. Maarten around the Saba trip? One thing the wife and I did that does sort of cost, but helped with luggage, is we got a good 2-week long deal on a place to stay in St. Maarten and kept it even while we were in Saba for 3 diving days; that way we could take absolute minimums for the flight to Saba. Of course I didn't have a DSLR rig back then, but one of the couples were were diving with had one and he took great advantage of it. Got some wonderful shots.