On lawn and garden tractors, they don't rate them in "PTO" hp because rarely is a pto used on those tractors, and most of the time they are gas engines. I don't actually remember the hp on that tractor, but gross was @ 24-25.
I don't believe the specs. and literature actually showed PTO hp. Yes, that is a Yanmar diesel and would have both ratings, just wasn't published.
On compacts, yes both hp ratings were used but not on the L&G tractors.
17, 18 was about right. The X495 handled a 4' rotary cutter "fair" if just cutting pasture, weight was more of an issue than anything. handled the 624 tiller pretty darn good though.
I believe the Deere pto gen has been discontinued anyways so only units already on the ground would be available. Possible opportunity to save though is someone is sitting on one.