Whats your objective?
Conserve energy or going as fast as possible? If its steep enough your going 35 mph without pedalling, adding 200Ws of pedalling isnt doing much difference to your speed. Less than 5 mph additional speed. Thats the nature of wind resistance. The power to overcome it increases by the cube(!) of the speed, meaning 2x speed is 8x power.
Imo, do what ever feels natural to you but know its more efficient conserving your energy to the uphill bits.