PA, JOHN
I also don't think it is an issue of the weight of the implement, but the drag created by pulling the disks through the soil. I am using a 4 1/2 VASSAR 2 row disk harrow with my 18HP Grey market Kubota in desert sand and it works well. But I sure can't get in a hurry. In fact I just spent a good part of yesterday harrowing my 2 acres of field. Yesterdays work was in dry sand, it does better in damp sand, don't know about other soils though. I would think 25HP should be able to handle a 6 1/2 but I am just guessing based on what my tractor is doing.
Wil