Welcome to the Apple Support Communities
The memory type you mentioned is the one that your Mid 2011 iMac needs, and a Mid 2011 iMac supports 32 GB of memory without any problem, althoug Apple says that it only supports 16 GB of memory.
Apple often puts a smaller memory quantity than the Mac really supports, and we don't know the reason, but the most important thing is that you can install 32 GB of memory, 4x8 GB of memory. You can buy the memory in OWC or Crucial (Crucial is cheaper and offers the same compatibility warranty as OWC).
If you need help installing memory > http://support.apple.com/kb/HT1423?viewlocale=en_US#1
Thanks for the great information. You mentioned "Crucial" as a source to buy the RAM which I am unfamiliar with. I was advised that "New Egg" is another overall decent vendor. Do you have your own personal preference between the two or perhaps some other company of choice? Really appreciate your advice. Thanks again....