Raking the mast has little to no effect on nose-diving, upwind or downwind.

Except that for slower boats that can't sail with the apparent wind off the breeze, raking forward lets the sails "breath" and generates slightly more power, which creates a greater pitching moment. This is only relevant for slower boats like one & two sail dinghies which don't generally have to worry about nose-diving anyway because they are fat.

Generally speaking, resistance, power and control will limit your speed.

Why do you need to de-power when your hull starts flying?