Hey Mike,
First of all, thank you for the DSDT, it is working perfectly and now I have network cards working.
I am in the middle of a project too, so I didn't had time yet to really push this board through, I was running a Z9PE before this board, but that ASUS board is a real problem, bad bios, unstable USB ports (at boot, not even talking OS here). But, when I was running the Z9PE I was able to get PM working under MacPro 5,1, MacPro 6,1 and such.
I would tend to stick with the MacPro 5,1 since I have dual GPUs (Nvidia 780 + Titan) and I believe that SMBIOS is more "open" to different GPUs. I will see how it goes with that... otherwise I was planning to switch either iMac 12,2 or MacPro 6,1. Thing is those two are sometimes problematic with the GPUs (specially regarding AGPM.kext, to get PM working on the GPU).
Regarding the MacPro 6,1 config, as far as I recall you can patch the AppleGraphicsControl.kext to avoid black screen and that problem is gone.
I will be able to conduct more tests today and I will let you know how it went, I will try to run mavericks clean and fully supported first, once that it's done I will give "El Capitan" a try and see how it goes (I really want to test the Metal API support).