Well I got to this thread a month too late

I only have 2 pedals.
I have a clutch button and DO NOT use auto-clutch (you cant actually turn it 100% off anyhow silly game)
I set the clutch sensitivity to the fastest possible (100% I *think* otherwise its 0%)
I DO NOT USE the 3,2,1,go rubbish, or the lights (lights can be unreliable on some addon tracks) and ALWAYS use the lap timer.
Hold my clutch button, put car into 1st and wait....
The exact moment (or as close as possible) the lap timer goes from --:--.-- to 00:00.00 I leave..
This is usually about 70-100% throttle which is based on the cars gearing and torque.
For example the Lotus Elite at Monza you have 100% throttle and never lift in the start.. you get almost 0 wheel spin.
However if you have the big Cobra or the mutha-trucka Corvette at somthing like Nurburgring Mullenbach you need to be a tad carefull

Thats about it... in pretty much any online racing I've mostly always made up a couple of grid spots, or if starting from the front, I've managed to get a small break. This was most evident in my V8factor league series run here in NZL, starting from the front row in almost all races, I'd have about 5-6 tenths on 2nd by the first turn.