Guvna, it's been two months. How'd the sulfuresque alt turn out?
According to the White Labs website, "high" fermentation temps can create a high sulfur level in your beer. So one possibility is that when you overpitched, the excessive quantity of yeast produced a larger exothermic reaction than normal. Your normal cooling methods may not have kept the ferment in the desired temp range with such a big yeast load.
I'd imagine that overpitching itself can cause extra yeast stress, apart from the higher temp. Add the two together, and maybe that's why it happened.
I think that's what happened to one of my lagers. I used most of a previous yeast cake, the ferment took off like a rocket, and the rotten egg smell that pervaded the whole house almost got me banned from ever brewing in the house again...
fortunately, most of the odor wore off and the beer is drinkable. I still have a few left. I'll crash chill them for a month and see if they improve.