PWM will affect punch, so long as it isn't a trigger full. Honestly, stock racing you pretty much set it to 1-2kHz if you have a ton of traction. But if you don't have traction and you are not grabbing a trigger full coming out of corners, then yes, PWM will have an effect. Lower frequency produces a touch more torque. This comes really apparent in mod, when I am running a 4.5 in mod TC, I set the PWM as high as I can without over heating the ESC, this helps calm corner exits down a bit for me.