Yes, flew the 9154's on 6.6 volts for a lot of years. All of the 4.8 only servos run fine on 6+ volts. When you get above 7 they start to act weird, but they will comfortably handle 6.6 with no problems. As I said, when those servos came out, Futaba only sold 4.8 packs, so that is what they recommended. Now it is almost hard to find a 4.8 only setup. You wont have any issues running those at higher voltage as long as you dont get closer to 7V.

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