I know this is an old thread, but this would be a good thing to know. 3.7 sounds high to me, but I would have no way of knowing without measuring or hearing it from the brewery. Dupont does seem to be on the high side of the carbonation scale.
I put 243 grams of corn sugar in a full sixtel (5.16 gal) and then bottled immediately. Beer temp was 65F. It fermented at 85F for a few weeks and then I let it cool naturally to 65 for 2 weeks. I assumed CO2 in solution @ 65F which would get me 4 vols for that corn sugar dose. Came out great, maybe slightly more carb than Saison Dupont but not overly so. Awesome head on that beer since it had 15% malted rye and 5% each of malted spelt, malted wheat and flaked oats. It won first place for Saisons in this year's War of the Worts.