I swim in the wonderfully chilly lakes of Ontario and Quebec, and I must say they get cold. However, on an Olympic swim you're going to be working up a fair amount of heat, so be careful you don't over heat. Peeing in the wetsuit is standard works pretty well. Get in the water a bit before the start to do some warm up so you aren't starting the race with the water in your wet suit still cold. Try to swim in water the same temp as you're expecting a few times first to experiment. Trying the heating packs in a race if you haven't swum with them in before in those temps could bring some surprises.