Horsepower is almost a non-issue using a bona fide Scandinavian logging winch. Your
B7100 will have adequate HP for most situations. Conversely, you will likely NOT have adequate 3PH lift capacity...while you could lift something like a Farmi 351, I don't believe the
B7100 would lift that winch when you had a log fully skidded in, and were ready to lift the winch + log, and proceed "down the road". Your front wheels would be heaven bound. Lots of folks use logging winches with smaller tractors...and then skid (with winch lifted and log attached) by using left or right rear brake to "steer"...not safe though!
The tractor horsepower ratings given for most Scandinavian winches is largely based upon the weight of a tractor - tractor weight increases relative to the size of the tractor. A front loader is a MUST when using any skidding winch. Common sense dictates that one must counteract the combined weight of the lifted winch + log on the rear with equivalent front end weight of the tractor.
Of course, you stated that actual skidding was not a primary concern...only getting the log to the tractor is the issue. If that truly is the primary objective, something similar to the Farmi 290 or 351 would be a very nice tool. If the stock 165' feet of cable was not sufficient, you could always use smaller diameter cable and accordingly have significantly longer cable length capacity. I have seen 351's using over 400' of smaller diameter cable....instant low lead system! Do be aware that if you do load up the drum with cable, and do not usually use that much cable, that the effective diameter of the cable drum increases, and accordingly decreases the line pull. The manufacturer stated line pull on a drum winch is based upon just a few wraps of cable on the drum...not a drum fully loaded with cable. It is for this reason that many loggers use lesser cable lengths - largely based upon their usual log to tractor or skidder pull distance.
Despite what others have stated in this thread...the winch will not impart significant forces onto your relatively small tractor...when the winch is in actual use, it is in a fully lowered position, and the winch's butt plate will contact the soil. The tractor's 3PH is, in essence, just holding the winch in a vertical position. By virtue of the relatively high pull point on most winches, the downward force on the winch will anchor the winch...you can "bury" a winch in this manner, thus further lessening the importance of the weight of the tractor.
Also, others have stated that "things happen quickly" with a winch. Perhaps they were referring to a positive engagement (geared) winch...but certainly not with a better Scandinavian winch using an internal clutch to transmit PTO power. If things are happening too quickly, common sense was not in use. Keep your PTO RPM's low...you don't need them for HP! If you need more power, then...and only then... increase your engine RPMs. Most long time users of 3PH winches use them at a near idle. If something is happening (log hung up on stump, log hung up on bank, tractor front end heaven bound), just lessen your pull on the engagement rope...things will go back to normal...and in a predictable manner.
The reality is that one can meter the line pull of a Scandinavian winch with suprising accuracy. Want to move that log one inch...no problem...just pull lightly on the winch rope and slip the winch clutch. Don't worry about frying the winch clutch in doing this either...I have NEVER seen a winch clutch fry with prudent long term use. The large backing plate on the winch clutch acts as an effective heat sink.
Hope this helps out. I've been using 3PH logging winches and arches for over 30 years. I suggest a larger tractor with FEL if you are going to actually skid logs. Above all, BE CAREFUL.