If the stall comes back at a true 4200 the ET and 60 ft reduction is going to be very good. How much is up to debate, but my WAG is .3 to .5,plus maybe some mph. Instead of 150 hp at the launch you will have what ever it makes at 4200 minus some loss for slippage. So it will pull that much harder all the way to when the car would have reached 4200 rpm with the old converter. Please post results when you can.