http://canberracruises.com/Maclean/Middlet...CommonFuels.pdf
heres an interesting report done by sydney uni. its 3 years old i know, but the info is probably still valid, and more importantly they produced results on a dyno in a controlled environment. finally some hard facts!
i recommend reading the whole thing, but a quick summary
if you want to use 98 octane fuels, then some ethanol blends show impressive power, if you dont want to use ethanol go with Caltex 98.
caltex 98 produced more power on an STI than BP ultimate 98, optimax 98, and synergy 98.
id like to see results on other cars, but the STI is a pretty good car to use. it adjusts the ignition timing dependant on what fuel is used and its a turbocharged engine.
ive always used caltex 98, because its whats closest to where i live, ive never had any complaints with it