Unless you are going to run a mower, my experience is that these tractors do not benefit from more than 10HP.
I specifically went looking for 10HP for my blade tractor.
I just read another post where a guy was slipping the clutch in second gear with 10HP pulling a plow.
I push snow in third gear with the 48" blade shown above, no lack of power with 10HP.
The clutch is mighty tiny, if you have loose soil traction that stops the tires from spinning.
Hydros' need more than 10HP, but for non-mowing, the lack of vibration with the 10HP is a great advantage. IMHO