I'm downloading the image now. I have a 2011 27" iMac and a MacBook Air. I'll install it first on the MacBook Air for testing, and then on my main iMac.
The iMac performs OK these days, but I really need to upgrade the hard disk to a SSD model. Not sure if I will be able to find anyone in Canberra to do it, or whether I will just bite the bullet over the next six months and upgrade to a new iMac. I can't quite justify the ~3k for that at this time, but as things progress it will become necessary