I'm from Vancouver Canada and most of the kiters here use Ocean Rodeo dry suits in the winter. This might have something to do with Ocean Rodeo being a local company but most people swear by them. The convienance of being able to get into and out of them easily and staying warm on the coldest days has most convinced.
That being said, I wear a wetsuit. I really hate the baggy feeling of dry suits (although I havent tried the new OR surf dry suit). Reminds me of sticking your hand into a sink while wearing a dish glove.
I wear a 5/3 with a thermal layer under and I rarely get cold, even when it's snowing. Gloves, boots and a hood are mandatory equiptment in the winter.