I just loaded and tested the 4k rpm launch control. This is definitely the "sweet spot." Generally, I would lose about 250-800 rpm when feathering the clutch to launch. This keeps the revs well within the powerband and the vehicle remains controllable (I was in Euro MDM). At 3500 rpm the car felt like it was dragging through the band. I haven't tested the 4500 rpm launch control file, but I think that will result in too much wheel spin and would eat into the available band in 1st gear.
'09 E90 M3 SG | VF620 SC | KW V3 | ARC Wheels w/AD08 | OnEighty Lights | BPM Sport coding | AA Catless Exhaust | BMW Performance Wheel | Recaro Child Seat
'13 X3 DSB with M Sport | H&R Springs | Gloss black grill | Coded by me