He didn't see a top speed drop off because he was running the high altitude prop. You have to look at the data and try to get a fair as possible comparison. If he had been running the stock non HA prop his starting top end would have been in the low 40's, I would think, and then drop into the high 30's. With my 45 I dropped from 42 to 36 - 37 MPH with the 5 blade. Not good for my use.
Maybe the 45 and 25 are completed different animals but all I know is the 45 is a barge and takes alot of power to go fast.