Point "2" better applies when the storage substrate is memory and operations are O(1) or logarithmic, because in that case, the time to serve the query is comparable small compared to the time needed to process the reply and send back the response. With an on-disk storage, I would go for a classic on-disk database setup where different queries are served by different threads.
LMDB beats all other "classic" on-disk databases for read performance. It also happens to beat all other in-memory systems for read performance too, since its reads require no locks.
