Depends on what you want, my Saison recipe that I responded with to your other post I used 28 grams for 10 gallons. I have doubled that much as well with good results in my Christmas Saison Noir (that beer was awesome). I have used much higher quantities when I wanted a real presence there, but for a Saison the trick is to have the spice in the background so that, when you drink the beer you say "Hmmmm .... what is that character?" If, when you make a Saison the person says "Hey, that's GINGER!" you screwed up.
Now, I used to make a Honey Gingered Ale with a Kolsch or a American Ale yeast and it was down right spicy.