Ditto Jon's answer and I want to emphasize it is equally true for PostgreSQL (VACUUM ANALYZE).
The only performance analysis that will help us measure scalability is that performed on installations with meaningful amounts of data (I think you pass this test) with statistics properly gathered as will be done for a production site.
Both DBs will generate horrible plans if tables aren't analyzed. Both will do so occassionally even if they *are* properly analyzed but not nearly as often.
