I have a 4s as well and sync my calendar and contacts to Outlook 2010. I have not updated from 5.1.1 as of yet. I was curious if you sync through iTunes and if so do you do that over the usb cable or wifi? I had seen in another post on this issue where somebody was using 2007 and upgrading to 2010 resolved but you are already there. Have you scanned your pst file yet?
iPhone 4S, iOS 5.1.1, Outlook 2010 USB/sync