The highest RPM you can without spinning your tires.
You won't know what RPM that is until you are there on the track on that surface and doing it. Really. There are too many variables. I would start at about 2000-2500 and go from there. Anyone that gives you a specific RPM that might work for them does not mean it will work for your combination and track conditions.
You launched at 5K with ET Streets and didnt break anything!?!? What do u have done to have it hold together because im pretty sure if I launched at that with my ET drags than my driveshaft would be comin throught the floor boards to say hello