Did you consider GCP Datastore as well?
It has strong consistency for a single "entity group", but eventual consistency for queries on multiple entity groups.
So by storing data only relevant to a single user in an entity group, you can have strongly consistent, atomic transactions on that group (albeit limited to 1 tx/s), and at the same time do global queries on all user data with eventual consistency.
Hint: if you have technical reasons for avoiding GCP Datastore I'd be very interested in hearing about them
In 2017 they will finally have datacenters in Sydney, London, Singapore, Frankfurt etc.