in terms of speed, you'd be better off launching at at least 3k rpm, but if the affects on the tranny are what you are more interested in, of course having ur foot on the brake with the rpm up to about 3k will affect that, you can burn out your torque converter if done enough times. Its not gonna be something that you will do 3 times and then ur tranny or converter will fail, but it over the life of the car, if done enough times, it will shorten the tranny/converters life span.