A Kubota
B7510.
I bought my 5' cutter from a Kubota dealer who also sold Land Pride. I had a 16.5 HP Deere 670 based upon the dealer's assertion that they sold these 60" standard duty cutters to
B7500 owners. Powerwise, the
B7500 and 670 were very close.
Land Pride recommended 20 PTO HP minimum (4 HP per foot) and I was running it with 16.5 HP which is about 3½ HP per foot (the
B7500 was about the same PTO HP).
The 670 did a fine job, so I think it's safe to assume the
B7500 (now
B7510) would do well too...at least as far as brush cutting.
The hindrance with the
B7500 or
B7510 might be the weight of the cutter if you wanted to transport with it raised. I could with my 670 (as long as the FEL was installed), but the 670 weighed a few hundred pounds more then the
B7500. However, even with the 670 (and my current 790), I towed the cutter more often then transported it raised. This isn't something you'd want to do any great distance though.
Anyway...the question was what is the smallest tractor that can run a 5' cutter. Well, the Kubota B7500 is the machine.
That's if we're talking new tractors. Used Deeres would be the 755, 855, 670 and 770. The pictures attached show the 5' Land Pride rigged to the 670.
I don't know where the 5 HP per foot number came from...I think it's one of those internet suggestions that eventually became "fact".