I really don't think you need to buy more yeast for a stout. The 011 would be my choice to keep a little more malt and body due to it's lower attenuation. The 085 will work great too and if you want to get it used before it gets too old I say go for it. I don't have experience with 051, but the 001 California Ale always seems to accentuate hops to me, something I don't want in my stouts. I hear Greenbelt does this even more. With a robust malty beer like this, I don't think you can really go wrong, it's mostly about what you like.