I think Royal Purple Purple Ice says to do a 20/80 mix so it can keep the water from freezing during the winter months. A straight mix of water with one bottle of one of these is the absolute optimal in terms of pure cooling, but the anti-freeze comes into play in the winter time. If you'd be willing to switch out to a mix during the winter, then yeah, straight water with WW, PI, DCB's or Motuls would yield the most impressive results. Just do NOT forget to add in at least 20% glycol during colder months to keep from freezing as that could have catastrophic results!
IMO, it's best to play it safe and do the 20/80 mix on your first maintenance interval (usually once every 2 years). Initially, no reason to waste good anti-freeze, just add one bottle to your system and go. When your 2 years is up, switch to the 20/80 mix and 1 bottle.
Most people just add a bottle in to their already 50/50 mix, as it's the easiest. It's what I did. Then wait the 2 years for the time for maintenance and do the 20/80 mix along with adding 1 bottle.
Price wise, Water Wetter, I believe, is the cheapest and I honestly doubt any of the others could give any significant advantage. And I disagree with the poster above about a car needing to run a certain temperature to be optimal. Heat is something every car battles against. Anything that can swing it a little bit in your favor is a nice bonus, especially during these blazing summers and most especially when you are doing some racing of some sort.
And yes, dparm, you are correct. The coolant additive become less and less effective the more glycol you add. But at 50/50 it still works well. As I said, I have a 15 degree drop across the board on a 50/50 mix. When I switch to 20/80 I fully expect even better results. And pure water with the coolant additive gives the absolute best results, but as I mentioned earlier, you're playing with fire (pun'ish) so to speak. If you go that route, you better be darn sure you remember to add glycol before it gets below freezing! No way would I take that chance myself.
To the OP main questions, yes, I would think this would also in some way help cool the tranny fluid, it just makes logical sense, since the surrounding fluid adjacent to your tranny cooler just below your coolant would be cooler, this could have some effect as to the temperature of the ATF passing nearby. I don't know HOW much, probably not a whole lot, but it should help at least a little, and therefore you would be gaining two benefits. At least that's how my logical brain reasons it. Though I suppose I could be wrong, as I often am. lol
