the coldest air temp i've ever launched in was probably about 54... (Florida) actually my poor daughter was with me on a 95 XP 800 and while she was off in college I had switched from a 96 xp with stock sponsons, to beach house, (oops, I forgot to mention that to her) so on her first turn at 40mph she got tossed 10 feet. I'll give her credit, she got back on and finished the next 2 hours w/o any complaint, except for the comments: "you coulda fkn told me about the sponsons"
Also did a cold weather run (ya i know what I consider cold...) up on the suwanee river I'm thinking it was mid to high 50''s and it was dam cold on the speed runs....
For me even with a neoprene dry top and board shorts, I'm thinking about 54 is the lowest i'll go, if I lived up north maybe i'd adjust that down to 49.