I have paddled in spring, but not winter. Not what I’d consider super cold, but brisk. Daytime temps in the 40s-50s. I wore my Kokatat Super Nova semi-dry suit with light-medium weight polypro bottoms & top underneath. Lightweight Smartwool socks. I was very comfortable. I was paddling Stillwater Canyon, Green River, so no whitewater. Paddling an Eddyline Caribbean 14, so not an entry level SOT.
I suppose if I wanted to paddle in colder temps, I’d be comfortable. I’d wear heavier layers underneath, warm gloves, and warm headwear. Maybe neoprene socks, or just thicker Smartwools. I’ve only paddled SOTs due to a non-bending knee, but I think re-entry with a SOT would be easier than a SINK…unless you can roll really well.