I have one and have used it down to 55F and I was toasty warm but then again, I'm not one who gets chilled easily. It's a very popular suit in the quarries and gunkholes around here. It easily handles excursions into colder water. It's a very comfortable (for thick neoprene) and extremely well made piece of kit. One of the Scuba Diver Girls has an excellent and IMHO very accurate review in her blog:
http://scubadivergirls.com/blog/?p=1482 .