I'm no macho dude. I like to be warm when I'm in the water, but I was HOT this Saturday in a 5 mil and I was out for 2.5 hours. I'm not a fatso either - 5'10" 170ish. Air temps were in the 50s and very light winds along with pretty mushy waves, so not a lot of duckdiving. Maybe I'll be cold in a 4/3 and I'll wish I had the 5 mil. A lot depends on the air temps and wind. You've stated that you have no cold tolerance. Obviously people differ and some have more cold tolerance than others. That's how some people can be hot and not lying about it with macho stupidity while you're shivering.