Gryadka is less than 500 but supports membership change :) yet 3 hours on it is quite impressive
One thing I think is worth touching on is the pipelining ability of multi-paxos that is missing when you have a single register with the Synod protocol. For key-value operations, it's not a problem. For a true replicated state machine, this can hinder performance.
In Replicant[1] I added pipelining to ensure Paxos was unlikely to be a bottleneck to replicated state machines. For complex state machines, the state machine becomes CPU bound.
What do you mean by pipelining?