[pbailis]

As a shameless plug, I might add that if you can model your network delays, you can use some modeling like our work on PBS (Probabilistically Bounded Staleness) to predict staleness: http://pbs.cs.berkeley.edu/#demo

I'd also add that the consistency related to ACID semantics from relational databases refers to transactional consistency, not replica consistency. Indeed, distributed RDBMSs often opt for strong (replica) consistency models, but there is no reason a distributed relational database can't be weakly (replica) consistent while maintaining ACID semantics on a single machine. Moreover, if the RDBMS must needs to be available in the presence of partitions, it must be weakly (replica) consistent.