Thanks for the link Denny.
"Usually, beers that are lighter in color (less than 12 EBC) are dosed with 100,000 cells/mL. Beers that are darker (more than 35 EBC) or have ethanol levels above 7% v/v require 500,000 cells/mL"
So if my math is right, 500,000 yeasties*20,000ml = 10,000,000,000 = 10b cells? Dry yeast contains about 20b cells per gram, so for a big beer I'd want 0.5g of yeast? I've been using 10g per batch, but after reading the powerpoints I think I'll scale that back.
I was going by the pitching rate Lallemand recommends for Champagne refermentation.
EDIT: It just occurred to me that since you blow out the yeast in the methode champenoise, autolysis isn't a big deal, but might be if you leave the yeast in the bottle.