The really tricky thing is this...

You can only drink a solution which is isotonic (same salinity as blood) or less salty than isotonic... why? Because if you take a too-salty drink, water will be drawn into your stomach and gut by the salt, and you will dehydrate. And since we really can't drink more than about a quart an hour, we can't take in more than about 400 mg of sodium per hour in sports drinks (I think Gatorade is 100 mg per 8 oz).

But, if you're losing salt in extreme conditions (like where I live, Houston, 95 degrees and 90% humidity, and bright sun) then you lose 1000 - 2000 mg per hour.

You can't shovel in the salt fast enough to replace it.

If you take a quart of isotonic solution per hour, you're doing the best you can. At some point, you just have to know when to say, "Enough! These conditions are too harsh". The long-term answer is better conditioning, so you finish the event faster and hit the showers.