One thing you're taught in road racing is that as an average, each time you shift, you lose 1 second lap time. Think about it, the faster you're going in 5th, the higher the RPM. The higher the RPM in 5th, the higher the RPM in 3rd. If you're going around 80, you're probably only going to have around 1000 RPM of power before you have to shift at redline. So, within the period of 3 or so seconds, you can potentially lose 2 seconds worth of WOT acceleration to shifting that you didn't need to do. Instead, I would recommend shifting at the 55-65mph range. While you may potentially lose a second that that shift, you have that much longer to wind out the engine again before shifting to 4th, and that may be all the time you need to get you far enough ahead to not lose whatever it is you're doing.