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 :
2011 27" iMac SSD upgrade + fan speed - Whats the current consensus? | MacRumors Forums
SSD or hard drive upgrade for iMac16,2 21.5 inch late 2015
How To Upgrade/Replace Mid-2011 iMac 21.5" Hard Drive To an SSD - YouTube
How-To: Now's the right time to swap your old iMac's hard drive for a fast new SSD - 9to5Mac