My late 2009 iMac 27", 2.8ghz Core i7, 16gb ram, 512gb Crucial SSD with Radeon HD4850 GPU is running macOS Mojave (thanks dosdude) like it was new. I've had it 10 years since new and has never let me down. Recently the bluetooth card has gone funky ($5 Fleabay) so I'll be replacing it soon. This model (2009-2011) is easy to open up and work on unlike the iMacs from 2012 to present. Plenty of useful life ahead. It runs cool thanks to dual SSD's inside (boot-optical SATA). They don't make them like this anymore.