probably be ok with a 3/2, but a 4/3 will definitely have you covered when it comes to warmth but not as mobile as a 3/2. if you are grabbing and poking and moving a ton while riding then you might have higher priority to warmth than stretch, its up to you.
i learned quite a few things about wetsuits on
http://www.pleasuresports.com/
they have nice descriptive videos on many suits and lengthy info on all the suits with up-front easy to compare stats, such as temp ratings.
pretty good prices too
another site that is nice when searching through and learning stuff is wetsuitwarehouse.com, but i like pleasure sports better