2011 iMac CPU Upgrade - will a Xeon work? Also how about a k2100m at the same time! - YouTube
Upgrading the GPU in the 2011 iMac - is it worth it? - YouTube
Apple opens graphics card replacement program for some mid-2011 iMacs - 9to5Mac
Original Graphics Video Card GPU Upgrade Replacement for Apple iMac 21.5 Inch Late 2011 Core i3 3.1 All-in-One Desktop PC MC978LL/A, AMD ATI Mobility Radeon HD 6750M, MXM VGA Board Repair Parts :
Upgrading an iMac GPU for METAL Support! Late 2009 – Mid 2011 Models - YouTube
Amazon.com: Valley Of The Sun 2GB Graphics Video Card Upgrade for Apple iMac Mid-2011 27 Inch Core i5 MC814LL/A MC814 A1312 Desktop All-in-One PC, AMD Mobility Radeon HD 6970M Replacement Repair Parts :
Upgrading the graphics in our 2011 iMac (first attempt) - YouTube
Amazon.com: Original Graphics Video Card GPU Upgrade Replacement for Apple iMac 21.5 Inch Late 2011 Core i3 3.1 All-in-One Desktop PC MC978LL/A, AMD ATI Mobility Radeon HD 6750M, MXM VGA Board Repair