I had a 10 gallon batch of Saison quit on me earlier this summer. Slightly below average temperatures in Los Angeles early this year were partly to blame. Also, some saison yeasts are very temperamental even when done at ideal temperatures.
I am such a bit fan of saison that we brewed another batch yesterday.
I was tempted to culture a Fantome yeast up to 10 gallon size, but got too busy. We were lucky to get a crop of yeast from a local craft brewer that makes a fantastic ginger saison (http://eaglerockbrewery.com/
I would think about adding some (half lb for 5g) Belgian candi sugar instead of table sugar. It just feels right. Keep your alcohol up and let it finish very dry.
Also, keep a pitch of WLP001 or equivalent around for the possibility that the saison yeast does not finish. The saison funk is usually born in the first day or two of fermentation and finishing with 001 will get your beer dry and still retain the saison flavor (or so I am learning).
Check out our blog (link in sig). There are a couple posts about our saisons in the first page or two.