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.