Most of my obvious sweating is done when I stop, especially after lots of climbing. If I keep moving, the breeze evaporates the sweat and helps keep me cool. Ten pounds sounds excessive, though I suppose if you're replacing with fluids right along, then they kind of cancel each other out, as the OP suggests. I think it's good to run a lot of water through your pores on a regular basis. Less need to find a place to piss, as well.