I use an
L4610, which is the equivalent model from the previous generation of Kubotas, on our 10 acres. For many chores, quite frankly, it's overkill for this size of property... tilling, boxblade, post holes, spreader, etc... would all be done just as well by the
L3130 -
L3830.
There are some tasks where the extra HP does make a difference... loader work, heavy bush hog mowing, pulling loads on hills, etc.
Just my opinion, but I think 45-50 hp is about at the top end of the hp range appropriate for this size of tractor. In fact, this much hp can tempt some operators to take on work better suited to heavier, full-size tractors... if you browse the archives, you'll see some threads where that may have happened.
That said, I have never found a need for more horses, which is definitely a luxury. I've never had to crank it up to the rated 2,700 rpm that brings the PTO to the industry standard 540 rpm, even in heavy bush hogging. For most operations, running the engine at 1,800-2,200 rpm provides ample power.
You could probably get by with less, but any one of the 4330-4630-5030 models makes a mighty nice package!