I would wait til at least 500-1000 miles before you start launching it. But when you get there, this is how I launch my 04' wrx. Its not an STi, but this might help. Slip the clutch out around 4-4500 rpms. Don't take too long, or you will smell that wonderful smell of a burning clutch. If you go to fast, it will either stall or be very jerky. You will know when you get it. If you dump the clutch, the car will bog with anything under 5k. I did it a couple of times before i was warned about the tranny and I would rev it up to 5500 and release the clutch and stomp on the gas. I wouldn't recommend this to a wrx, but I know that the STi tranny is a lot stronger so I'm not sure. Maybe someone with an STi could chim in. Anyways, good luck!