I sail a dinghy on an inland lake and have a drysuit and wetsuit. At this time of year in the UK, the water temp is probably around 5 deg C. At the weekend we capsized and unfortunately my dry suit was not quite zipped up correctly. It was enlightening - just a couple of pints of very cold water inside the suit made me effectively useless for the recovery, my muscles started cramping fairly quickly, and had we spent longer than the 10 minutes or so it took to recover, I would have been hypothermic.

The summer weight wetsuit, whilst keeping me slightly warmer than a compromised dry suit, would, in my estimation have given me a few more (15 - 20) minutes of useful activity, but on no account would it have been a survival suit.

The drysuit would normally give me 30 mins to an hour of useful exertion in water of that temp, with perhaps another hour of gradually degrading performance.

The other point to remeber is that these suits are hot out of the water. I didn't wear anything useful under the dry suit as the sun was out and the air temp at 14 deg C would have made the suit unbearable. Wetsuits are similar - any form of exertion out of the water and you will potentially over heat.

So, in summary, no way will a wetsuit be a useful survival suit in the lakes unless you could be sure of rescue in minutes. A dry suit will give you a couple of hours. A liferaft is infinately more useful - you must get out of the water to survive.