Not sure if I have followed this correctly, but if you intend to parbuckle a 7,500lb log I hope you video it for us all to see!
I've done it many times, but never bothered to video it. I move 10 - 15 cords per year with that trailer, with just a few free Saturdays per year to do it, so speed and efficiency are the only solutions.
I drop the tree, buck it into 15, 30, or 45 foot lengths, based on diameter and what I think that 7500# trailer-mounted winch can manage to pull. Then I hook my winch to the butt end with either a choker chain or tongs, and drag it to the tailgate. There I will either buck it to 15 foot lengths, or shorter if needed to get under 5000#. My trailer payload is 5000#.
Remember, it takes many times less force to pull a log than lift it, so if the terrain is right, I’d bet I can easily pull 10k# logs with less than 5k# of force. At that point, the biggest problem is keeping my truck planted.
I don't usually take time to take pictures, but here's one red oak that was right around my maximum payload (probably 5200#), where I did manage to have to time to take pictures while waiting for a buddy to arrive and help re-install the tailgate that fell off my trailer while loading.
(Maybe you are sectioning it first before loading?)
Yes! I prefer to bring home 15 foot lengths, because it's a perfect multiple of my final cut length, and because my trailer and storage are both set up for that length. But whenever an oak log is larger than 30 or 32 inches, I need to cut shorter in order to not violate my trailer's GTWR rating. It's a 7k# trailer that came in at 1800# from the factory, and to which I added maybe 200# in winch and batteries, leaving roughly 5k# for payload.