I went in a few days ago. Air temperature 2°C, water 6°C. It was my new wetsuit's first outing*.
Despite wearing neoprene gloves, when I emerged my fingers were immensely painful with the cold. Curiously, my toes weren't. Couldn't make sense of that. I drove to my pal's house and picked her up, and then another pal was awaiting us at the beach. Before we went into the water, conversation was normal and measured. Afterwards, all we seemed capable of was guttural noises and "FAAACK! That was cold!" My two accomplices were not wearing wetsuits.
I think I might put a pair of Marigolds under the neoprene gloves next time. I have to say that I doubt that there will be many occasions on which those precise conditions occur this winter - we were in the water at about 8.40am. I suspect that the water was especially chilly after having crossed a mile or more of mudflats that had been close to 0°C all night. We were swimming about an hour before high tide, so I think it may have warmed up a little had we swum later. But my pal has this irksome thing called a Job, and she had an online meeting at 9.30, so we couldn't hang around. I don't think we spent much more than 5 minutes in the water.
*Because of a long delay between me paying for the wetsuit and it arriving, I had one on loan and used it two or three times. Last week's dip was a great deal colder than anything else I've faced. The previous coldest was 12°C for the water, about 10°C for the air.