Yar for any car the fastest launch can be achieved at 5000- 5500 Rpm.
Unlike others who just made stupid comments ill tell u specific steps how to achieve a really quick launch.
1) At stand still put car in 1st gear. Keep ur clutch pressed, Then press and release accelerator really quickly. Make sure that ur rpm meter is hitting nearly full rpm each time u press accelerator. As soon as it hits u take ur feet off the accelerator and repeat this thing 4-5 times at least without letting the rpm meter to go down below 5000 rpm.. Its like pumping ur car. When u do it for the fifth time then maintain the rpm at 5500 rpm and
2) Quickly release ur clutch. As soon as u release ur clutch press the accelerator really hard to the ground.
3) Now it depends on how powerful ur car is, what tires u have installed in it, etc etc. Therez a gear ratio defined for each car. Like when i use to race with my honda city 2002 i had the following gear ratios
0 - 57Km in 1st gear
58 - 95 Km in 2nd gear
96 -125 Km in 3rd gear
126 - 157Km in 4th
158 - 180Km in 5th.
I didint go above 180 Km/hr
4) Depending upon what ur car's gear ratio is stretch ur car to the fullest and changed the gear at precise speed ur car is capable of going in that gear. By my gear ratios u can tell how perfectly i knew my car. Its not that i had to look at the meter to change the gear. I could change the gear just by feeling when my car wanted the next gear.
So KNOW UR CAR LIMITS....
I hope u appreciate the tips that i gave u. Do let me know when u try these steps. I used to race at devils point in my black city 3-4 years back. Its was great fun then I really miss that time.