I can attest to the patch install running without incident on an Early 2008 Mac Pro (3,1) and being relatively easy (ignoring any non Mac video card issues), 90% of it being the same as doing an in place upgrade using a usb stick. High Sierra On A Mac Pro 2008 – Patching Thoughts There are a large group of older Macs that have fallen foul of this cutoff (most of them being released in and around 2008), thankfully a rather enterprising Mac Rumors user going by the name of dosdude1 has written a patching tool to bypass this limitation. However this does appear to be a software cutoff point rather than an issue with the hardware required to run it. High Sierra on a Mac Pro 2008, technically the last officially supported version of macOS for the Early 2008 Mac Pro is El Capitan.
