I came across the site blitz.io which will test your web sites performance. It is free and easy to use.
I tested it against www.apriorifarm.com and www.zebulak.com. www.apriorifarm.com performed magnificently whereas www.zebulak.com performed so poorly it locked up my server and I had to do a hard reboot just to get it back.
So why is one good and the other bad? All the settings and environmental factors where the same for both web sites. Zebulak has a larger home page. It turns out that zebulak had one setting that was different.
On the W3 Total Cache settings the Page Cache Method should be set to Disk:Basic
Mine was set to Disk: Enhanced.
Performance -> General Settings -> Page Cache -> Page Cache Method: Disk: Basic
The following are the reports for the three test cases.
SUMMARY www.apriorifarm.com with W3 Total Cache ANALYSIS DATE : 3/31/2012 This rush generated 6,867 successful hits in 1.0 min and we transferred 6.71 MB of data in and out of your app. The average hit rate of 109/second translates to about 9,481,655 hits/day. SUMMARY www.zebulak.com This test was made with no caching turned on DATE : 3/31/2012 ANALYSIS This rush generated 13 successful hits in 1.0 min and we transferred 784.22 KB of data in and out of your app. The average hit rate of 0.40/second translates to about 34,366 hits/day. You got bigger problems though: 99.80% of the users during this rush experienced timeouts or errors! TIMEOUTS The first timeout happened at 5.02 seconds into the test when the number of concurrent users was at 21. Looks like you've been rushing with a timeout of 1 second. Timeouts tend to increase with concurrency if you have lock contention of sorts. You might want to think about in-memory caching using redis , memcached or varnish to return stale data for a period of time and asynchronously refresh this data. SUMMARY www.zebulak.com This test was made with W3 Cache Turned on and Page Cache set to Disk: Basic ANALYSIS DATE : 3/31/2012 This rush generated 6,942 successful hits in 1.0 min and we transferred 11.45 MB of data in and out of your app. The average hit rate of 110/second translates to about 9,556,742 hits/day.