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 :
Apple iMac 27" Core i7-2600 Quad-Core 3.4GHz All-In-One Computer - 4GB 1TB DVD±RW Radeon HD 6970M (Mid 2011) - B
A Pragmatist's Opinions: 2011 iMac Upgrade
HOW TO: Upgrade The CPU from an Intel Core i5 to an Intel Core i7 on a Mid- 2011 21.5inch iMac - YouTube