I always always always were a wetsuit. Even in Palau with 85 degree water I got chilly after a few days of 4 dives a day in a 3mm fullsuit.
It all depends on how much you move around, and for me drift diving means very little movement so I get cold faster.
Feb-March water temps, anything below 80 degrees, would be a 5mm fullsuit and a beanie on my head. Yes. really.
And I have NEVER been too warm on a dive... if I were, I would just pull the neck out slightly and flood the suit. Problem solved. On the other hand, I have been cold on dives, no way to fix that. Better to wear the suit.