Thanks for the input.
I wouldn't be posting or shelling out for a computer if I wanted to do 'trust-me' dives, although the operators' attitude is, of course, 'trust me'. Yes, computer rules are fine for buddy dives, but I've been told that it's "follow the DM" on larger-group dives, and I don't have experience with the politics of potential dive-profile conflicts with the DM (I imagine it'll be go-no-go). I deliberately chose a conservative computer... and plan to follow it.
One op offers a 75-80 ft dive in Cozumel (day trip) for 35-40 minutes, which is pushing it (not ALL at 75-80 ft, presumably), some do reverse-profiling and there's a Cancun wreck dive offered at 90 ft. (WWII boat), don't know for how long. I'm diving every day for 5 days, >1 day of rest before flying home, with as little day-to-day reverse profiling as possible.
regards,
Sy