"As all good marine engineers know, the maximum speed a displacement hull can attain is a direct function of length."
An excellent observation and, after looking up Froude's law and running some calculations (and torturing the numbers until they confessed to the conclusion I wanted), I think I have it all figured out.
The absolute best position for diving is with the head tucked down between your arms, which should be extended straight ahead as far as they will go with the hands clasped together. You won't be able to see where you're going in this position, or to read your gauges, and you might swim your hands right into the mouth of a great white shark, but you'll be making good time and saving air all the way.
I think this posture will extend your "waterline" to the maximum extent possible, and in a diver of about my size (6'3" and 200 lbs.), I figure I can boost my effective "hull speed" maybe 20% before the drag curve starts to climb up on me. I don't know what I'm going to do with all that additional speed, or where I'm going to end up (it would be nice to come back to the boat at some point), but everybody in the water will be able to spot me. I'll be the amazingly fast guy with his hands (or even his head) jammed into something he didn't see coming, and shouting for somebody to come help pull him loose.