Aporte original por: Claude ,
My answer is a bit late but I had kept my mid-2007 iMac at Snow Leopard and it performed well. Migrating to Mountain Lion saw a noticeable decrease in performance and I opted to install an SSD. I put in a Samsung 840 Pro series, 256 GBytes SSD in my iMac and saw a remarkable performance increase. I followed the disassembly instructions on iFixit and the only problem encountered was related to the mounting bracket. The bracket has to be full length. In my case, the metal adapter had undersized holes with different thread pitch. I re-drilled to correct size and re-tapped the screw holes to work with Apple original hardware. I also used Chameleon SSD Optimizer, which seems to work like a charm. The SSD is by far the best upgrade I have ever done.