I'm not sure where Futaba got crossed up on their servo voltages. One theory is that the 9252 was originally designed as a tail rotor servo to be used with a Futaba gyro, and the gyros DO NOT operate on 6v.

When Ann Marie Cross was still with Great Planes, she assured us that the 9252 would work at 6v for the reasons given. I mounted 4 of them up and used 6v to complete the radio installation. No problems at all. Then Ann Marie left, and the new Great Planes tech people had a rather hard line stance over strictly following the Futaba voltage guidelines.

Deciding discretion was the better part of $300 worth of servos, I switched back to 4.8v. I liked the (presumed to be) .10 speed at 6v...plenty of torque even at 91 oz in for my application.