Thought I'd try V power.

[VNA]

Given that a higher RON fuel has a more controlled burn, timing can be adjusted to make the most of the burn cycle to ensure you get the most out of the fuel? I'm not saying the fuel has more energy, just that the timing can be adjusted to make the most out of the burn. Given the more uncontrolled burn of a lower RON fuel, I would assume that at least some of the energy is wasted.

Nope, you want to use the lowest RON fuel you can get away without pinking.  The anti-knock additives sap a little energy from the fuel.  Remember the RON rating is a measure of anti-knock property.

Engine design (and probably ECU software) will factor in a lot on this I imagine. I agree that an engine may not NEED a higher octane fuel to function, but surely that is like saying you don't NEED decent tyres - the car will still perform its function. But upgrading either can be beneficial - I'm not saying it definitively, just that it is possible.

On that basis, can I recommend you use this water for your coolant.  http://www.veenwaters.com/index.html