Fuel - 98RON or 98RON with 10% Ethanol

[mixja]

I'm wondering which of the two should I use?

I've read on forums in Australia where they've found that a 98RON Ethanol blend over there has better tuning capability (up to 4 degrees more timing than 98RON petrol-only) on the Holden (Chevrolet) LS2 engine.

I've filled up the last two tanks on the Ethanol blend, MPGs have dipped by about 10%, I think the car feels a bit quicker although can't be certain.

Any science behind this?