Well, if I can throw my 2 cents worth in: For what its worth, I have only JUST completed my NAUI OW Cert here in the Bay of Fundy. Water Temp for all of my check-out dives was a balmy 47*F (It doesn't get a whole heck of a lot warmer than that in the height of summer either...). While I found the water a bit cold on my exposed face (I like the vasoline on the cheeks idea..I think I may try that once the water temp goes down a few more degrees...) I was quite warm and comfortable for the duration of all of my dives (I have a healthy layer of biological insulation to add to my neoprene). I stopped noticing the cold on my exposed cheeks within a minute of going below the surface, and my whole body remained warm throughout. Now, mind you, I was using a 7mm full suit with boots, gloves, and a hooded 7mm vest, but even so I was initially (prior to my very first OW dive) concerned about whether or not I would be warm.
My Instructor was using 5mm five finger gloves, and I had 7mm three finger gloves. About half way through my first dive, I noticed that my hands actually felt almost hot. After discussing it with him, he suggests that I could probably do quite well with a set of 5 finger gloves as well, and I will probably take him up on that advice for the increased dexterity.