I made my 2011 iMac feel like new by getting an external SSD thunderbolt drive and using that as my boot disk. Running applications and the OS off of it really sped everything up, and it worked so well that now with my new iMac I am still running things off of the same external drive. Whats great, you can still access all your files on the old internal drive and if you ever need to travel you can run your "iMac" on any thunderbolt-enabled mac.