Rusty: What we encountered 50 years ago with the percentage pull, A and Super A were quite handily pulling 3 times the tractor. Limiting factor was traction, never ran out of power. H and Super H were very close, with H running out of power and Super H running out of traction. The C and Super C plain ran out of power at around 2.5 times their own weight. I can't remember anyone stumping the M or SM for power, they always ran out of traction, even when they pulled with added weight.
In this type of pull, all tractors do better with no added weights or chloride. I remember one year some guys showed up with Oliver 77, Cockshutt 40 and SM loaded for bear with weight. Tractors straight off the farm were smoking them. This is what I like about the percentage pull. Not much farming done where load comes on tractor 50' into the pull.
Several years ago I went to a slow tractor race at county fair with my SA, There was a variety of Farmalls, Cockshutts, couple of MF, Oliver and Deere. Cockshutts smoked us on that one. Surprised me, I was thinking those MF with dual range would have it. Cockshutt 20 won the slow race.
We didn't use up our allotted time and fair officials ask us to do anythig to hold the crowd in stands. They had a stone boat with 100# and 200# weights. Some of us knew our weights and some didn't. We drew straws to see what order we'd pull in. You guessed it, lone little Super A had to go first. They hitched me up, asked how much weight I wanted to start with. I told them 6,000#. Well this 100hp modern Deere came in with a jumbo pallet of weights. Ton on each one, by the time he got the third one the ring anouncer was on his case about the fact the SA was going to pull 3 times what the Deere could haul. There was a lot of laughter in the crowd at my thinking I was going to pull 6,000#. Crowd changed as I walked away with 6,000#, and the ring anouncer really got on the Deere guy parked there waiting to take weight away so I could pull it. Then he had to go for more weight. The puller could add weight in increments of 100# or 200# until it stumped him after the initial pull. I next pulled 6,400#, then I uped it to 6,800#. I was starting to get some slippage. I next went to 7,000#, by this time in a bit better ring ground I pulled that easier than I had the 6,800#. They added 200# more and I pulled that however they rulled me out. I hadn't heard this but apparently every one agreed you were out if front wheels came off the ground. The Cockshutt 20 with wheel weights and chloride spun out at 7,400#. He and I were the only two lifetime farmers. The rest most of them had farm backgrounds but hadn't been on the farm in 20 years. Most of them had tractors, as they were when they bought them, 40 plus years old. My Cockshutt friend and I then stood back and watched the rest. Some had mis matched tires, chloride in one tire, tractor not tuned right, etc., etc. The two largest tractors that night, an H and a Cockshutt 30. None of them pulled a 1,000# more than SA or Cockshutt 20. I was in there at 2.97 times my own weight. 3.06 if you allow the 7,200# pull. 50 years ago I would have been given a chance at 7,400#. Cockshutt 20 guy would have been close, he probably weighed 2,800 which would have given him 2.57 at 7,200. I doubt if anyone else pulled twice the tractor weight. I stand by my opinion, operator ability has more to do with winning tractor pulls, be they percentage pulls or modern day pulls, than the tractor. I base this on pulls I've watched.
I've never taken part in modern day pulls. My 1066 was one year old when modern day pulls came to our town. IH dealer wanted me to enter. My tractor was 60 miles away with duals on and pulling down $600. per day on custom work. I said I'd take the 560, and they advised stock couldn't be more than 20% over rated hp, and they would be using a dyno. I told them they could shove their rules were the sun don't shine. Anytime I've looked at pulling since, too many childish rules. For example pull officials say I can't use my 130 one point fast hitch for pulling.