I'm running a site on an Ubuntu/Apache/Django/PostgreSQL stack. We upgraded our server recently from 1 processor with 2 Gb total RAM (with 0.5 Gb of that RAM assigned to memcached) to a new server that has 2 processors with 4 Gb total RAM (with 2 Gb of that RAM assigned to memcached). However, when I looked at Google Webmaster Tools, I found out that the average page speed has worsened from 5 seconds to 15 seconds.
Why would performance get worse with a hardware upgrade? What should I check and tune? Is this more likely to be a problem with memcached, Apache, Django, or PostgreSQL?