I've used 565 a few times, and the last one I used it on was a high gravity saison (8%) that included some crystal malt (which I've stopped putting in saisons for perhaps obvious reasons). I kept the temp around 70F for four weeks primary and bottled at like 1.010 (I think) which was as far as it ever went (bottles have been the same carb level for 4 months or so). What I got out of it was something that tasted an awful lot like an abbey ale. None of the "Dupont" characteristics that come from a 100% Pilsner/low final gravity/perhaps hotter fermentation. Lots of malty sweetness and a very subtle complex fruity yeast character that I think would work well in a dubbel, sort of reminds me of Chimay. So I'd say ferment it fairly cool, perhaps mash it medium/hot. It'd work pretty well.