I prowled around the test page a bit, & the numbers are really not good
at all (pitiful, really) if you compare numbers to Lyc powered RVs. The 'best' numbers from the latest chart he supplied (copied below) show 151 kts (173mph) tas at 9.3 gph (56 lbs per hr). That speed is roughly what Van claims for a 160hp -6A at 55% power (7.3  gph) at 8000 ft. That's a 26% penalty even if you ignore the 3,000 ft altitude (lower drag) efficiency advantage. At 11,000 ft & that fuel burn, he would  be going around 200 mph with a Lyc.

Since there are 2 big variables (plus airframe/cooling drag) in this equation, you can't tell how much blame to assign to the engine or the prop.

Don't be seduced by the *potential* advantage of a controllable prop. It's already obvious that the cruise/top speed numbers are much worse. I'm a bit too lazy to dig this deep, but you should also compare his climb rate/fuel flow numbers to Van's fixed pitch numbers. Do you really need a climb rate in excess of what the a/c can supply with a fixed pitch prop? If not, the only remaining reason is a drag brake for landing. That's the one area where fixed pitch RV's suffer. High sink rate low speed descents into emergency landing zones are a lot more difficult to achieve, but the -9's already lower landing speed than a -6 should help you there.

Charlie