Probably like yourself, our turbulence speed is 290/.78 on the 757.
Having said that I would always prefer to be a little fast in turbulence, especially if it gets worse .8 Mach is a nice comfortable speed in the 75.
You are not going to break anything and this Mach will give you a good margin above low speed stall if you start losing speed with wave action for example.
Going too fast is easy to fix, but if you run out of thrust at altitude with steadily decreasing speed you only have one option
