Average speed and avg revs is not enough to give you a properdrill.
A very wide ball park guess would be a 3.5" x3.5" or a 4"x3" or 4", but muc mor eis needed, like height above the midline.
I'd suggest going to your driller or someone who has seen your game and knows your ball speed, tilt, rotation and the conditions you face.
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"None are so blind as those who will not see."