I agree with BC.

10g for a shaft would be almost negligible difference in swing speed.

I am thinking of going from a ~120g shaft (TTDG) to a ~70g shaft (Accflex). This should result in, at most, 5 mph swing speed increase (based on MOI and a fixed amount of energy that I can "put into" a swing). Assuming this was a linear relationship, this would translate to 1mph per 10g.

I have seen your other post about your Launch Monitor results. You will not notice the loss of that 1mph (according to Wishon this equals 1.4 yards!).

Hopefully, the 70g shaft for you will result in better control/accuracy.