72 by 85
I went with the "standard" prop Van recommends for the 180 HP RV-4 (72" diameter by 85" pitch). I have the tall gear on my RV-4 and have absolutely NO problems with ground clearance. I'd be comfortable with a 74" diameter prop if I had to go that route.
I hope some day to convert to a Whirlwind RV-200 prop, but will probably keep it as is for now.