Large batch INSERTs / UPDATEs and DELETEs Performance problem
Is vacuuming slow because you have inadequate IO throughput, or just because it is throttled too much?

The default throttling of autovacuum is not suitable for very write-intensive servers.  You should probably decrease autovacuum_vacuum_cost_delay or increase vacuum_cost_limit.  And I routinely set vacuum_cost_page_hit and vacuum_cost_page_miss to zero.  Page misses are inherently self-limiting as the vacuum process can't proceed until the page is delivered; so there is little reason to add intentional throttling on top of that.