I selected a site that I have had in production for some time, but recently upgraded to Drupal 7 & Commerce Kickstart 2.4. The problem was that some of the heavier coded sections of the site would take minutes to load. The front page could take 3-6 seconds to load, and other user pages could take as long or longer. This is a low traffic site.
Test the site on different platforms.
I created a new hosting account with my current host provider to give them a fair shot.
I setup nearly identical Ubuntu Virtual Machines on two hosting providers, Amazon and another.
I installed this site on all three servers.
I used pingdom.com and gomez.com to test. I went with Pingdom as my primary tester as I could setup interval testing around the clock.
Pingdom reported Amazon response speeds averaging 100ms better than the identical Ubuntu server and 1400ms better than my original hosting provider.
Using Amazon, Front page response times were cut to sub-second responses. Heavily coded pages load in seconds vice minutes.
Even hosting four low traffic Drupal sites, Pingdom is reporting 300-500ms front page responce times when testing all sites at a five minute interval.