Maybe you saw my comment yesterday re hot weather riding on the Yahoo Hay group. Here in Saudi where it does get rather toastie-warm I found that using denim/kevlar (so I don't wet leather) and cotton under, it I could keep somewhat comfortable using a water backpack with a hose down my shirt.
At, say, 100 mph and 120DEGF you can't possibly hold enough water or sweat enough to make up for the heat being transfered to you by the wind directly on your skin. It sounds wrong, but just keep enough air flowing through your clothes to get the refrigeration effect of the drying cotton and it'll feel like you've got AC.