Suggestions for a 80-90% Granny Smith Blend?

I'll be making a cider from primarily Granny Smith apples as I can get a good deal on a couple of bushels locally. I'm looking for a tart, dry cider and I plan on splitting my batch using WY4736 for half and going for a wild yeast ferment on the other half.

Does anyone have suggestions for a small addition (probably a general grocery store apple) that would improve a largely granny smith (80-90%) cider?

I've read posts on the forums here that suggest a blend of apples with around 50-60% Granny Smiths. And a few mentions that a pure granny smith cider was "too tart".

Thanks for any suggestions.

Toss in something from any other variety of apple. A sweet dessert apple will give a refreshing and light cider, preferably something aromatic like a McIntosh or one of it's hybrids. A more tannic apple will result in a more full bodied cider, these will probably be harder to find but try and find some golden russet or a traditional variety like Dabinett, Brown Snout etc.

Thanks for the ideas, I'll see what I can find in the stores.