The NFL is using "cooling" gloves for some of their athletes. Turns out, core temperature is even more of a determinant of ability-to-exercise than being able to bring "food" to cells.

Forgot to look at your mass on the way into this post, but if you're at all large and/or insulated, you're getting MUCH better cooling in the water.

have you read Swimming to Antarctica, or Grayson, by Lynne Cox? She doesn't directly address your situation, but they're interesting takes on cold water swimming.

Only problem is, if you're regularly exposed to cold water, your body WILL lay down a layer of protective subc. fat as protection.