Thanks for the clarification Scubadada. I have previously asked about 2 tank afternoon potential at CBBR and the response from one of the DMs was that most of their customers were older and that they would not be interested or able to do 4 tank dive days. It would make for a pretty long day for the DMs as well. Their job doesn't end when the dive boat lands. I personally find that if I do the usual 3 tank profile, I am near NDL by the end of the third dive using conservative Suunto algorithm anyway. When I was there last March there was no nitrox available, so on air, I was uncomfortably close to NDL by end of third dive.
I guess if you stayed shallow it would be fine, but the Brac wall starts at 45-60 feet so one tends to go deeper. Diving LC with a generally shallower wall would be no problem for 4 tank dive days.