I have a Mid-2010 27" iMac that is having hard drive trouble. I'm thinking about putting an SSD in it, but I'm curious about whether or not it's worth it. The Mid-2010 iMacs made the cut and were able to upgrade to Sierra when it came out, but there will obviously come a time when they will no longer make the cut. For all I know, it may still be eligible this fall, but there's no guarantee. Here's my question: How long can I reasonably expect to at least receive security updates once my machine is no longer eligible to upgrade to the latest operating system?