I suggest one with at least 1 GB of video RAM. It even includes a script that will check and fix the bootloader each restart which means you can install system updates without having to repatch your system each time.
It is correct about the 32 bit EFI on these systems but there is a workaround with a re-written bootloader for the MacPro 1,1 that will enable you to run El Capitan (last OS before Sierra) flawlessly on your Mac Pro.
It sounds like you have a mac pro 1,1 like mine with Quad core 2.66GHz processors.
