if you stick a cheap emerald, or gems etc ignition module on ( I am sure there are cheaper ones about,) then you can run a specific ignition advance on the warm up map. you could put plenty of advance on the main map, and set the warm up map to lower advance settings.
The extra advance is due to the higher octane level. more advance=more power. you could just tip octane booster in the petrol, then you could run the same advance
Just a thought. but the bio-ethanol E85 that morrisons are selling now is about 112 octane it hink thats the same as lpg. so with the advance can you run that instead of petrol and get more power for less money???