My view on suits is it's better to overdo it a tad. You can always fall in and to cool off. Once you're cold though, you are cold.
I wear a 4/3 and I wear a steamer top underneath. That top underneath is the deal maker. Without it, I get cold, with it, I am totally warm.
I also wear a hoodie gig when it's sub 60. Without it, my head gets real cold and that's where you lose a lot of heat.

I can't imagine only wearing a 3/2 full. That's me. Let's see what the others guys say.