Just another post and perspective on this topic. My wife and I have been kayaking for about 18 months. We started in the summer of 2019 on Lacamas Lake (just north of Portland in Southwest Washington State). We really enjoyed it and invested in more serious boats (Eddyline Stika LT and ST) in January of 2020. We continued paddling through the winter.
We knew the lake would be cold during the winter, so we purchased Farmer John / Jane wetsuits and used them through the winter. In late January, I capsized and got to experience immersion first hand in my wetsuit. After the fact, I went back to measure the water temperature. It was in the low 40s. As I am writing this now, clearly I survived the experience. However, I can say it was extremely unpleasant. Wetsuits do not keep you warm initially. Instead, they absorb the cold water and hold it against your body, which ultimately lets your body heat warm the trapped water. In short, when you first hit the water, you get the full shock of the cold. It was indeed shocking and disorienting.
Another factor that many beginners (including myself) overlook is that swimming and maneuvering while wearing a PDF is far slower and more cumbersome than just plain free swimming. As a result, between the cold, slight panic, and added difficulty with the PDF, I was unable to re-enter my boat, even with my wife holding it steady.
Fortunately, I was close enough to shore that I was able to swim awkwardly and slowly and get out of the water in about 10 minutes. At least the effort warmed me up to the point that I was not shivering too badly by the time I hobbled out of the lake. My wife towed my boat over to shore and I eventually got back in and paddled back to the dock which took about 1/2 hour. Even this was somewhat uncomfortable since I was still quite wet.
That experience was sufficient for me to say never again. I survived, but it was scary and miserable. I like winter paddling as it is quiet and frequently uncrowded. But I would not willingly repeat this experience.
Fortunately, I have the means to purchase a drysuit, which I did that same week. In the interest of ensuring that I would have no additional surprises, I suited up with a thin layer of fleece under the drysuit, slipped on my PDF and jumped into this same lake which was still in the low 40s. It was an absolute night and day different experience. There was no initial temperature shock, I stayed warm and dry the entire time I was in the water. It was an almost surreal feeling. I was floating in water, but at the same time I was completely dry. Despite the very cold water, I was totally relaxed and comfortable. After a few minutes of the strange floating, I slowly (swimming with a PDF is still awkward) swam around the dock to the boat ramp and walked out of the lake like the creature from the black lagoon.
The bottom line of all this is that for me, even if I could paddle safely in cold water with a wetsuit (something more substantial than my Farmer John), I would not do it because of the initial cold shock and the discomfort of staying wet after a rescue. Conversely, I now have no hesitation to paddle in the coldest of conditions while wearing a drysuit with appropriate insulating layers underneath.
Others may disagree, but for me, there is absolutely no substitute for a good dry (or semi dry) suit for cold water conditions.
Good luck and stay safe