Trevor, denatured is the easiet to tune with. This mix (actually about 10% water) is very forgiiving for lack of atomization, and activation point(s). If it works for you, use it.
When switching to a more 'watery' mix, try more timing, or switching to 2 smaller nozzles.
Everyones combination is different, so it's not suprising that different mixes are needed to achive the desired results.
Atomization is key. You need small nozzles to get this. Unfortunately most people have single stage systems, so 1 small nozzle while getting good atomization, often will not deliver enough water to accomplist cooling. This small nozzle will work to say, 18-19 psi, but will run out of cooling power at higher psi.
Some of the best systems I have heard of use 2 small nozzles for the first stage (activation point of 5-8 psi) and a second stage activating at 15 psi, using about 2 thirds of the combined nozzle size of the first stage. Full pump speed is preferred, and a 50-50 mix is easily achieved. Past research has shown the 50-50 mix works best, if you have the proper set-up. Regulation of the volume of delivery should be done by raising, or lowering the size of the nozzles, or the number of nozzles. Pump speed should always be as high as possible.
As Steve Hill has said - atomization is key!