I was just in for an hour and half with my (womens, last years model) xcel xzip, 6/5/4/3 and was fine.The water is now 39 degrees, the air is about 30 degrees, no wind. I have a full poly skin undersuit underneath, 7 mm on feet, the only thing is my 5 mm gloves don't hold up, they are old; ordered new xcel drylock 5 mm gloves but probably need the lobster claw. So, overall, not that bad to last an hour to an hour and a half in the middle of January out on Long Island with this suit!!
I did well over 2 hours in my 5/4 drylock, no thermal shirts or anything underneath, and when I got out, I was still quite warm. only reason I got out is because the waves were small I got tired of waiting for sets. that just says even more for the suit, because i did a lot of sitting around rather than surfing which would have kept me even warmer. If i wore a 6/5/4 with poly shirt underneath, I'd probably have to let water into my suit to stop me from sweating.