Warwick, you've bought the safest option by far and James has hit the nail on the head too. I use a 5mm wet suit regardless of the cold or conditions with dive booties as well. When it gets cold I put a PVC jacket on over the top to break the wind chill factor. I also wear a thermal top under the suit to keep me warm or to protect from the sun. I also believe in wearing a self inflating life jacket - the Sospender type - regardless of the conditions. You can step into that unseen hole even on the calmest days. As I swim like a rock, it's by far the safest for me. Even with out the Sospender the wet suit will keep you afloat.