That's an impressive undertaking! I never made more than 10 gallons of mead at a time... I can't imagine how much room this operation is taking!

Wyeast was what I used, too. The only difference I've noted in the dry vs sweet mead yeast is that the dry has a higher alcohol tolerance - meaning it'll ferment down further than the sweet will (eating more sugar, making it "drier"). Alcohol kills yeast, so if the fermentation finishes sooner, the mead will theoretically be sweeter.

The sweet mead has a alcohol tolerance of like 11%, and the dry has a tolerance around 18%, IIRC. The sweet mead is also supposed to impart a fruitier flavour, but I've never compared the two side-by-side with identical batches, so I couldn't say.