As you may know, Mac OS X Lion dropped support for 32-bit Intel Macs. Mountain Lion also removed the 32-bit kernel and EFI bootloader. However, it's possible to get Lion running on 32-bit Macs by swapping out the kernel, the bootloader, and the Finder, as well as some drivers (kexts) and...
UPDATED ON 12th February 2018:
Feel free to use this thread to add your own discoveries or benchmarsks:
Searching Google for
Meltdown Spectre performance "Sierra" "SSD" "read" "write"
shows this:
Mac:
Measuring OS X Meltdown Patches Performance...