So I finally pulled the trigger and got an SSD drive for my iMac (mid 2010, 27", 2.8Ghz Core i5 w/8GB Ram). I Left the existing 1TB HDD in place, to use as storage. Installed a new Crucial 512GB (I think they just call it a 500GB) SSD in place of the optical drive, which I never use anyway. After installing it and powering up, everything worked as expected. It gave me an alert that it could not recognize the new SSD, but gave me option of formatting, which I did. I then downloaded the High Sierra full installer, and performed a clean install on the new drive... and switched the startup disk to this new installation. I can unquestionably say that performance is outstandingly better now. Many apps, especially my iPhoto library, aren't a real pain in the arse to use any more. Much much more responsive. But in the day or two after, several times upon waking the computer from sleep (by pressing key on keyboard or hitting mouse button)... it didn't respond right away... and twice it told me that the computer had rebooted do to a sleep/wake fault error. I was about to start googling what to do, when after that point it stopped having any issue. I've now gone three or four days and not had this happen again.... so I'm thinking that whatever caused that has hopefully cleared up. I opted to leave my iTunes file on the HDD, and moved the iPhoto file to the new SSD. I don't access the iTunes content as much, and all of the video stuff takes up so much space. At this point, I'm not thinking a RAM upgrade is necessary, and I'm glad I went with the SSD upgrade first. Definitely seems like it was the weak link.