For a handgun that weighs in the range of a standard 5" Government model 1911, I find that an IWB holster is much more comfortable to carry for 12+ hours a day, versus an OWB. The lighter guns, such as a Glock, or S&W M&P (and similar polymer frame guns), an OWB rig is fine. A well designed IWB holster provides a more stable and secure option for the 1911 and definitely makes a difference when you carry every day.
That is why I personally carry my 1911s in IWB rigs more than any other method, on a regular basis.