There is some eternal law that guarantees that since you have prepared carefully, you will never have to use it. Good idea on the dry suit. Around the northern Channel Islands, where the water is usually rather cool (48-65F), there is an interesting correlation. People who go into the water wearing wet suits survive, those without them or the equivalent don't, if immersion is more than a few hours.

The most extreme example was a guy in a full wetsuit who drifted for more than twenty-four hours, finally fetching up on an oil platform, quite hale and hearty..