How Shocking is 55 degree water with a wetsuit and cap???

Somewhat shocking. The first few minutes are a bit tough, but if you've got your wetsuit and swim cap (preferably two caps) you'll be fine once you get going.

give yourself a lot of time to warm up, in the water if you can.

Quite shocking IMO.

I did it and it was very shocking, the air temp was 40 and the water temp was 55. I swam in high school ( 22 years ago) so i did not expect the panicky feeling. Hopefully that will get better as i do more of these.