Agree with everyone above LOL I'd shift at 400-500 above peak, at least for 2-3 and 3-4, often find that a very early 1-2 can make a light car/deep gear quicker.
In fact, in a 5.13 1/8 mile big block Chevelle, we got quicker and quicker by lowering the launch RPM to 3000 and shifting the 1-2 at as low as 4500, (roller BBC peaked at 6500) but that car is unique as he overgeared it with a 3.43:1 1st gear with the 5.13s. The more we dropped, the quicker the car got until he tore the rear out of it. Unfortunately it scared him as it got a little sideways and I can't get him back to the track
However, the driver determines where the shift light needs to be, my Chevy guy needs it set at the HP peak because he moves slow LOL, but an automatic with a ratchet shifter and a good driver with the shift light in his line of sight, might be 300-400 or even exactly at the 400-500 mark