Any size drill will work, so use whatever is convenient. The size of the hole will control the rate of flow, not the pressure. It will be a lot simpler to use a Tee upstream of the flex line fitting rather than mess around with the bleeder screw. You'll get exactly the same pressure either place.
Once the brake components stop moving as the wheel cylinders and calipers get the friction material into contact with the drums and rotors, the pressure is going to equalize, so you'll need to be very quick on the trigger looking at the pressure differential.
Jerry
