I don't know what rpm you should be doing but the ratio of the 300CE should be higher (less engine rpms) than the 300SL. The 300CE has a 3.06 ratio from 91 on. Up to 90 it was 3.27. The 300SL has a 3.69 ratio with the automatic and 3.46 with the 5spd. The 300SL has the 5spd auto which is odrive so it could wind up with the higher over all ratio. The TDM gives a 240kph max speed for the 129 and 232kph for the 124.051 car, so the overall ratio must be higher with the odrive tranny even with the much lower ratio diff.
Bosch Master, ASE Master, L1
33 years MB technician