loads of posts about this already, but from my experience, the engine seems to respond quicker and pull better across the rev range.
I now use it exclusively.
I also put Millers octane booster to take the RON upto 100, but that didn't seem to make much difference.
Go for the Optimax - it works for me - not massive, but genuine noticable difference and it keeps your engines internals so much cleaner.
Proven to work in various tests and most who have used it on here agree.
Less pinking is all good. Basically its a higher RON petrol which means its less suspectiable to being ignited too early in the sequence from heat. and its only ignited by a spark. Therefore it develops the right ignition at the right time and gives more power as a result. If it ignites too early then it pushes the piston back down when its on its way up.
Its 99.3 ron when mixed with Millers Octane boost,and there are some scooby owners that swear it causes pinking in their highly tuned Imprezas,one such guy,Dingy I think,researched this to the enth degree,and er,came up with a load of techy stuff i can't explain.