Leaded race gas will actually hurt performance unless you're tuned for it because of the way it burns. A lot of wrx people run mixes of c16 and 100 unleaded so the dmg to the sensors is far less. That being said... with proper tuning... I've seen 60-70 whp gained out of running it in ~300whp wrx's.

For example, jinxproof... who a lot of you honda people are familiar with just dyno'd his wrx at 320whp on 93 and 380whp on c16.