What temperature do you need a winter wetsuit for?

The thinnest winter wetsuit would be a 4/3 wetsuit I think. I don't really think that 3/2 can be categorised as a winter wetsuit. So... how cold must the water be that you will need at least a 4/3 winter wetsuit?

I'll just copy the temperatures from my other wetsuit post (Which wetsuit do I need):

TEMP: 59F–64F / 15C–18C
A good 3/2 full suit, 4/3 wetsuit is better.

TEMP: 54F–59F / 12C–15C
4/3 wetsuit+ booties, If you surf 54F a lot get a 5/3 wetsuits.

This is aproximately it, for more info check the link in that post that I mentioned before.

How thick wetsuits are there?

I always wondered this...even if I like to think I know a lot about wetsuits I know that the fattest thickest wetsuits are not found in surfing but I guess they are found in diving. Diver do not need to move so much as surfers do so if the wetsuit is extra thick that gives them no problems. And sice they do not move a lot they need thicker wetsuits. So how thick is the thickest wetsuit?

For surfing a thick wetsuit is generally called everything over 4/3 mm. 5/3 or 5/4/3 is still pretty standard. Then 6mm wetsuit is the top comfortable limit and I know there are some 7 millimiter wetsuits, at least there used to be. Bot are very rare. Are diving wetsuits thicker?

The catch here is also that when the water gets so cold that even divers need a wetsuit thicker than 7mm they usualy go for dry suits. And not wetsuits thicker than 7mm.

So there are not many of them, but we managed to found a 8 mm thick wetsuit that is mass produced. Then we managet to find someone that claimed that he had an 9mm Xcel wetsuit. And then we found someone who knew a guy who knew a guy that had a 11 mm wetsuit. That must be crazy to wear if it exists.

I'm not even sure if you can move in it :).

So anyawy - let's say that the fattest wetsuit out there is 11 millimeters. If you have any other data, let me know! :)