downunder,
Actually, it sounds reasonable that two different engines that advertise the same rpm range and HP ratings should spin the same prop at the same rpm, but it often doesn't work out that way. With little 2strokes, their timing, compression, and spinning mass often produce different torque curves that do peak about the same value but with different loads. The engines won't spin the same props the same rpm. A 65 would be designed to put it's peak power into the 12-13" props and do it at moderate rpm. A 46 would be designed to spin 11" props at higher rpm.

If I had to bet, I'd bet that the 65 would be spinning faster than it's design peak with a 10-6. But the 46 wouldn't be as far off it's design peak. And after messing with a bunch of 46AXs, I'd guess the 10-6 would be a bit small for it's envelope as well. Mine seem best with 11-6s. For those two to be compared with one prop, the prop ought to be within each engines envelope, and as far into each envelope as possible.

When you run most 2strokes outside their design envelope, they often don't produce power worth spit.