This year I've had 3 drivers.
I have an 82mph driver swing so right on the bubble of a lite and regular flex shaft in most brands.
One was too stiff and I was constantly hitting it low and to the right (usually either a push or slice).
One was too flexy; when my timing was right I hit it good, but I was spraying it all over including bad mishits.
The one I am using now seems to be a good mix in the middle and its going much straighter and trajectory is good.