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The comparison was done several years ago. Bass had built custom midsections and gearcases for the tohatsu 50D2 model so it could race in Stock Outboard “D” class. The test is very interesting for a few reasons.....the Mercury 44XS was a race prep top running motor. The dyno numbers show the great improvement and why racing prep makes a difference. The Tohatsu is not race prep. It is bone stock just as it was shipped. You wonder how much better it would be when it was race prep.
Both these motors are a production outboard. The racing outboards like Yamato develop their maximum horsepower at higher Rpm...example 33 hp @ 6600 rpm. That’s the reason they perform so well on raceboats.

CBHP = Corrected Brake Horse Power.
RPM. Merc 44xs tohatsu 50D2
3500 ........27.5 .....................34.6
4000........ 33.8 .....................40.8
4500 ........40.4 .....................45.3
5000........ 45.9 .....................47.8
5500........ 49.5 .....................51.3
5750 ........51.3 .....................55.3
6000........ 52.5 .....................56.2
6100........ 53.1 .....................56.2
6200 ........53.5 .....................56.5
6300........ 53.8 .....................57.0
6400 ........54.0 .....................57.2
6500 ........54.4 .....................57.8
6600........ 54.3 .....................57.0
6700........ 54.7 .....................56.1
6800 ........54.5 .....................55.5
6900 ........54.6 .....................55.1
7000......... 54.3 ....................54.4
7100 .........53.7 ....................53 39.
7200 .........52.1 ....................50.1
7300 .........51.1 ....................48.4

Remember these are horsepower at the crank shaft. A production outboard is rated at horsepower at the prop shaft. Both these powerheads as production models would be advertised as 50 hp at the prop shaft . Even at 7000 rpm these stock ported motors make good horsepower. You can see how the race prep mercury performs better at the higher rpm.