That's one part where having multiple completely independent processes is a disadvantage to just having threads. I never benchmarked this, but I always heard that Postgres processes are expensive and you should always use a connection pool. But this is probably more noticeable on the DB server side, where each process uses memory. I never used it myself, but PG bouncer might be useful to you in this case.
The number of requests still feels slow, and it isn't clear to me from the blog post whether that is DB limited or CPU limited on the application servers. Even with writes on each access Postgres should still be bored at that kind of load.
