I'm sure many of the regular posters have visited this site, but if not check out the fine testing of various shotgun rounds in simulated dry wall. The results of this trial and the other great info available on the site may help you make a decision on what to load for home defense.
The Box O' Truth #3 - The Shotgun Meets the Box O' Truth - Page 1
4. I "racked" the shotgun several times during the tests, and no bystanders lost control of their bowels.
Conclusion: Racking a shotgun will not make the bad guy faint.