I'll give my two penneth on neoprene wellies... I bought some Grubs 'Frostline' ones late last year at a cost of around £65. I thought these would be the answer to me hating walking anywhere in traditionally styled wellies (I always suffer from socks slipping in them). Having worn the Grubs a few times now I can safely say: They are by far the comfiest welly boots I have ever worn and are very, very comfortable, BUT!! They DO NOT keep my feet warm. I have fished a few times with air temp between +5 and -3 and my feet have been numb. I have tried wearing with normal socks only, 'technical' socks only, normal and technical socks together, normal socks + 2 x pairs of technical socks. My feet were still cold
Last time out it was about 4 degrees air temp and I tried a pair of heat holder socks with them, this seemed the best combination.
Anyhow, in summary, I have not found neoprene wellies to be warm. But they are very comfy