I remember him telling me that a rule of thumb was about 5% power loss for a manual transmission, 10% for a Deere power shift, 20% for most others and 25% for hydros.
Test reports of January 1997 of 4 tractors, both powershift and synchro models of Deere and Fendt in 120 hp models, showed different numbers:
Tested were:
Fendt 312 with fluid clutch, 21 speed synchro, 125 hp
Fendt 512 with fluid clutch, 44 speed 4 step powershift, 125 hp
Deere 6400 synchroplus, 16 speed synchro, 105 hp
Deere 6400 powerQuad, 24 speed 4 step powershift, 105 hp
PTO efficiencies were:
91.9%
89.3%
87.4%
85.7%
drawbar pull efficiencies were:
79.3%
75.8%
72.8%
69.9%
The Deere powerQuad lost allmost 30% of its power in the transmission !!
Note: The actual difference in fuel consumption was less, because the Deere had a slightly more fuel efficient engine than Fendt.
Note 2: a fluid clutch as used in both Fendt models, causes about 2 to 3% power loss.
Building a tractor transmission with 95% efficiency is a utopia.
Back in the days of low pressure, high flow hydraulics when IH built some hydrostats, the efficiency was closer to 60%. Modern hydrostatics couldnt pass 75% efficiency.
In college we had a 4255 that we dynoed at 130 PTO Hp, and a 7120 Magnum that was 150. Both with power shift. The 4255 would literally run rings around the larger Magnum.
A Deere 4255 weighs around 6470 kg and the 7120 around 7810 kg. (weights of the European versions, USA versions may be ballasted 2 ton more !) The 7120 SHOULD put out about 180 engine hp.
taking the average of 13% power loss measured at the PTO for powershift tractors, the Deere should be about 150 engine hp. The Magnum might have a problem, causing it to not deliver the horses that the factory promises, but its likely that the Deere powershift is more efficient.