In my stock 09 my best launches are when I slip the clutch at 3500, then as it's about to bog put the clutch back in slightly, at this point the car is rolling. Then I rev to 4200 while slipping the clutch less and less, the go WOT right before the clutch catches 100%. If done right it's super smooth, feels like a jet, and does limited wear to the clutch and drivetrain for such an aggressive launch. I'd call it a 2 stage launch.
Maybe I'm a ratard but if I do a slight slip launch at 4k my clutch never catches completely and can roast clutch all the way to redline if I keep the throttle down (which I don't). Anything around 3k and it's bogstown. I'm gonna go out and practice. :-[
I got a good vid on my youtube channel got to therealsubarudude, or type in 2010 wrx launch you mite like it I like to slip the clutch a little at like 4-5k then drop it but not dump it know what I mean lolcheck it out, tell me what you guys think?