Talked to the good folks at Hitec.
The 7955 has different circuitry AND motor than the 5955 (Cs-170). The 5955 was not hi-res or had the G2 circuitry like the 7955.
The 7954 has a different gear set, different motor, and different circuitry than 7955.
Essentially the 7954 is a completely different servo than the 7955. I am betting the torque ratings are just estimates from the engineers, because the 5955 was never as strong as they said. So aside from similar ratings at 6v, they are all different.