Right now the data I have sitting in Azure Tables for something I would like to have use KVP once gridwide keys become available is using about 840KB for ~1300 entries, I would assume once converted into JSON for each entity it would be roughly the same.
The thing I would like to see the most is a way to visualize the KVP, that is really the only plus using outside storage has for me at the moment, as the KVP is far more convenient!
EDIT: Exporting my Table Entities to JSON resulted in smaller file size of 791KB