You need a queue in front of your database irregardless of write latency. Otherwise you tie your availability to database availability as downtime (even for upgrades) is often unavoidable and network problems are common.

Dan gave a pretty good talk about the high-level details of how/why postgres a couple of years back: https://www.youtube.com/watch?v=NVl9_6J1G60.

One reason of why pg is that SQL is really powerful for building complex queries.