If you don't want to change the iMac's internal drive, another possibility that's worth exploring is an SSD external drive connected via Thunderbolt. Using a with the OWC SSD, we connected the drive to the 2011 iMac's Thunderbolt port.

The iMac's benchmarks were similar to the results with the SSD installed internally, with the exception of one test--the large file Zip test, which took nearly twice as long when the SSD was attached via Thunderbolt. Other tests results that were faster with an internal SSD than with the stock 1TB hard drive maintained their speed advantage when the SSD was attached externally. The benefit here is that the SSD is much easier to connect to your Mac and is accessible if you want to use it with another machine.

After testing with the Mercury Pro 6G SSD, we upgraded the memory in our iMac from the standard 4GB to 32GB of 1333 MHz DDR3 RAM, using an OWC memory kit. We booted with the SSD, ran the same benchmark tests, and found that the extra RAM did not make a noticeable difference. In fact, the iMac with the upgraded RAM scored a 323 overall; the same score that the iMac with the stock 4GB of RAM.