my friend and i spent plenty of time trying out different RPMS and clutch engagement, and what works for US is 3500 when racing against most cars. but if the car is 4wd then we launch at like 4000-4200. Also when it comes to depressing the pedal we smoothly/slowly depress it as if we are leaving a street light, dropping the clutch is havoc on the clutch. my teacher in manual transmassions class (@ wyotech) said dropping the clutch as most do is like getting kicked in the nuts really hard by surprise, hahaha. he's the one that i also heard say to smoothly depress the pedal.
also i'd like to add that in my steering & suspension class that i finished my teacher there said that when it comes to launching that dropping the clutch also kinda depends on tire size if your running 245+ then it's better to drop the clutch as far as times go.
just thought i'd add my part to this thread =P when it's late at night go to a stop light intersection and practice. reason why i say stop light is because you can practice your reaction time.