I'm in the same predicament... was diving a 2/3mm shorty, but after 1.5 weeks of 2-dives a day average, I was getting chilly.DiveMaven:I must be part Hawaiian then....I won't wear anything less than a 5mm full suit year around on Maui.
After our trip in April, my husband has finally agreed that he needs to have a little more warmth, so he's going with adding a vest to his 3mm full. I'm guessing he got cold for the first time since not only did we dive everyday, but we did two of Ed Robinson's 3-tank Adventure charters, and by that third dive he was feeling the 75 degree water.
When I go back, it'll be a 3mm fullsuit, if not a 5.