Reasons:
This all sounds good but now that I have had a chance to really compare the two and adjust the map to adapt to it. (it needed massive changes to timing and afr's - way beyond the quick map that I ran at Gary's when on a 10% mix).. I am excited about the real-world effect of this fuel and have been able to notice the difference in the drive characteristics.
Why is E85 a better fuel ?
Ethanol and is a very turbo friendly fuel for many reasons.
1. It has a much higher evaporative cooling power than gasoline so the intake air charge in the cylinder is significantly cooler that it is with a comparable mixture of gasoline --- that means higher VE.
2. Its octane as blended in E85 is about 100, its blending octane when added to gasoline is rated at 118, so it is a very cost effective octane booster.
3. Ethanol burns faster than gasoline but has a slightly longer ignition delay during the slow burn phase of combustion so the engine does not do as much negative work fighting rising cylinder pressures due to large ignition advances. The total ignition advance for E85 is almost identical to the ideal advance for gasoline so it does not cause the ECU problems when you mix them.
4. At proper mixture you actually are releasing more energy in the cylinder due to the higher quantity of fuel you can burn. ( Ethanol can burn effeciently at much richer mixtures than gasoline can) That means about a 5% increase in energy release all by itself.
5. Peak combustion pressures are actually lower for ethanol than for gasoline but the cylinder pressures stay higher longer, so you have more (longer) crank angle that is usable by the engine. This lower peak cylinder pressure also helps with detonaton control.
6. It will, at proper mixtures lower EGT's by around 200 deg F, but due to the higher quantity of exhaust gas products it produces you do not lose any spool up (in fact I would wager spool up is better).
I filled up a couple of jerry cans from morrisons and have mixed it now at 20/80 with tesco 99 and love it

The lower figures are from between the 490 bhp runs at APT and Zen, the higher figure is on sunday using the adapted map. (all are wheel figures and using the same stretch of road, same fuel level, same gear and almost identical ambient temp)

I will be getting it properly dyno'd this week to see whether the dyno shows a similar improvement.