Not surprised by the gains. in my FD RX7 i saw some major reduction in water temp when i switched to WW and distilled water. Which in turn lead to a reduction in oil temps.
For those who aren't hip on how water wetter works this is snippet from a great article I bookmarked
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There are also additives on the market specifically meant for systems that run 100% water, like redline’s water wetter and motul mocool. These products also claim to improve the cooling capacity of straight water to reduce running temps. This is because there’s more to cooling than just the heat capacity of the coolant. What occurs on the boundary between engine parts and the coolant is also important. This is where the additives come it: they reduce the surface tension and “wetting” capacity of the water, which will make a slight improvement in how well heat can be transferred from the block to the water.
Most marketing and testing for these products compares a 50/50 water and ethylene glycol mix to pure water with the additive, and show dramatic reductions in coolant temperatures. Most of these gains actually come from the added water content, and not from a magical additive. However, there is still a benefit to use them because in addition to improving the heat transfer ability they have anti-corrosive and lubricating properties.
Things you should know about coolant | hellafunctional
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As for the antifreeze portion, I think it's a good idea in Virginia (85/15 or 80/20 should be more than enough though). If you garage it all winter, you are probably safe even with 100% water.
However, as a word of warning: On that same FD RX7 I lost a radiator after taking it over to a friends house, staying overnight, forgetting about the 100% pure water and leaving it outside over a cold NC winter night (vs usually garaged). So there is some small risk on that side, particularly for street cars.