For what it is worth. A slight reduction in the amount of coolant versus distilled water will increase the capacity to dissipate heat. There is a reduced protection from freezing as a trade off though.
The Environmentally sound coolants have proven excellent alternatives for my extreme use boat motors that rely on heat exchangers. Not nearly as toxic and very safe for aluminum. I don't understand why the manufacturers have not made the switch yet (unless it is cost). If I remember correctly the safer stuff is Propylene Glycol vs. Ethylene Glycol.