Without meaning to stray off topic but it is relevant to the same subject
I run distilled water/anti freeze mix coolant in my 2.8 since getting it back running earlier this year. Noticed it does run hotter - temperature guage is at a 1/4 now as opposed to previously 1/8 on the guage. It goes up to about 1/2 when required to work harder on open road then I reckon thermostat opens and it returns to the 1/4 mark so not concerned about it. I've also got quite an air flow restriction (number plate, winch) in front of my grill so I reckon that's what the issue is.
Kept my eye on it at the last picnic and it stayed at the 1/4 mark all day long when playing - lower revs and only going up the rev scale for a short period when required to climb the slopes.
Got the idea to go for distilled water when changing the coolant on my daughters Fiat Punto - Fiat handbook specified distilled water. Thought that can't be a bad idea to run with distilled water rather than tap water that could contain higher impurity/hard water elements.
I did check on tinternet and it does appear that distilled water does have a slightly lower boiling point.