I havne't launched my WRX... BUT I did have a very fast DSM with AWD.
People recommended a 4500RPM launch, and that worked sometimes but I had better 60' times with a 5500 launch.
The AWD launch is essentially a pass/fail. If you get it just right it will shoot you like a sling shot and not burn your clutch.
But if you get it wrong, your car will bog down and you'll spend the rest of the race playing catch up. If you're at a track and time is the game, you're better off just driving "normally" to the end and trying again - no sense in driving it that hard for a time that's not going to be accurate because of the poor launch.
Proper AWD launching takes a few, or several practice runs to find what works for your car.
Done right it's one of the best car feelings in the world. I used to take on friends as passangers and surprise them with it at stop lights (light turns green.. quick rep and slip the clutch and off we go). My buddy Jason was holding a two-way radio to poke himself in the eye because he wasn't expecting it. (this was during our youth days, we traveled as a group and used radios (aka walkie talkies) to talk to each other and warn of potential dangers, both road and the law enforcement kind).
After the "ow! my eye!" he said "oh my god, do it again".