I did a dive 3 weeks ago in 39 degree water (Indiana) with 7mm suit, 7mm boots, dry hood and 5mm gloves. 24 min bottom time. The only part of my body that got cold was my hands...but then they just went numb. The worst part was the (almost excruciating) pain in my hands when they started to warm back up. I’m considering getting a pair of XXL mittens to wear over my 5mm gloves.
You can also try wearing a 3mm shorty under your thick suit to keep your core a little warmer.
I will only dive in water that cold if the air temp is reasonable (like 50+) since the absolute worst part is stripping out of a wetsuit on a cold, windy day!
One thing to note: consider using a sealed 1st stage in water that cold. At the very least, make sure you are very proficient breathing from a free-flowing regulator.