Every time stuff like this comes up I wonder how much the people having issues would be willing to share - because every time I've fought with the postgres query planner, it eventually turned out what I wanted to do had massively worse performance* because of something I didn't take into account that postgres did. And each time, once I learned what that thing was, I was able to fix it the right way and get the query plan I was expecting, but also with the performance I was expecting.

* Usually I've been able to force query plans by disabling whole operations for a session, such as disallowing "sort" to make it use an index. The real fix in this case, for example, was to use CLUSTER to re-order data on disk, so the correlation statistic was close to 1 and postgres wanted to use the index instead of table scan + sort.