Apollo fin and sail range

[Crash]

Remi I find the fin size on my Apollo quite critical. Although its fantastic in light winds as soon as it blows I find you must get down in size, I use a 68cm with my 7.8 lightening then when it really blows I drop down to a 60cm and it just blasts along. Im a beginner getting into straps just fine but not carve gybing yet. As my experience grows will I be able to hang onto the larger fin longer or should a change down be automatic as the wind picks up?