Get a buddy to ride with you on the highway. In 3rd gear make a run putting it to the floor for about 6 seconds and have him watch for knock, then let off. Start working your alky setting down a little each time you make a run until you see an air/fuel ratio of about 11:1. Then you can start increasing boost again watching carefully for knock. Remember leaner is meaner (but only to a point). Double check me though on my advice; it's been a while since I've been racing.
I remember going to the track and my wife told me black smoke was coming out so I started reducing fuel pressure and upping boost. Of course I was running C16 so knock was nearly the last thing on my mind. And all I had was a scanmaster to watch O2 and KR.