Check this:

fastlane.com.au/Products/Nulon_octanebest.htm

wonder how Miller's compares? Anyone know where Nulon can be bought here?

Fast 4s Magazine in Australia also did a comparsion. They ranked Methol Benzine (Toulene) second and it was cheaper to use. MB is the only additive Subaru Australia approve of for use in the WRX and STi. They did do studies with other products but found them wanting in various ways. Stick to MB and save money.

But how do you know how much to use and what octane does it raise SUL to?

Martin