My numbers from the article are correct, are they not? Plus that was with a large solid FT cam and pretty decent compression ratio if I remember correctly, and it was still lower by 9 hp average below 4500 rpm.

I went and looked up my dyno data for my 500 in motor. From 3000 to 4000 rpm, the SD was down on average 20 lbft torque, and 12 hp. Down 26 lbft and 15 hp @ 3500. As would be expected, it did make a touch more peak hp, and carried it longer past peak.

I've been doing this a long time as well, and I have not come across what I would call any crediable evidence that supports the age old belief that the SD is just as good down low as a dual plane.