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.
'13 35i M-Sport X3 | JB4 Stage 1 | BMS Intake | H&R Springs | Gloss black grill | CF Wrap and Coded by me | Recaro Child Seats
'15 M3 DCT AW/SO | RKP Diffuser | P3 | M Perf Spoiler | iND Exterior Trim | Recaro Child Seat