Long post, but please read. I have the exact same motherboard as you, and I indeed do have 10.13.2 running perfectly - SpeedStep, C-States, P-States, GFX, Sound (ALC889,) Wireless (BCM94352,) and even the FireWire port built in (works out of the box, surprise cause uses a Texas Instruments chip) The trick for me was to enable EFI in the bios. Unlike other motherboards of the time, all intel motherboards had a compatible UEFI 2.0-2.1 implementation, as Intel was the designer of the original EFI specification. Just enable EFI and you will be able to install Clover onto a USB/disk and boot from it natively. Once you have booted UEFI, that eliminates some hurdles that one would have if one used legacy boot. My system is in my signature (Hack Pro) - E5645 OC'd to 3.21Ghz with 12GB of ram - hopefully yours is similar. I have attached my clover folder - but please, don't just copy it before you use it. Go over it and see if there is hardware you might need to tweak for on your install.
I have the minimum and maximum multipliers for my cpu SSDT hardcoded - yours is
different, might want to use clover configurator to change it. Also, I have
textonly enabled. This will speed up boot and
for this particular board, allow you to use verbose mode.
If you use the gui, then you will not be able to see verbose mode - it's a console-mode quirk of this board that I had to devise myself. Lastly, I have removed the serial number, for obvious reasons. Generate your own with clover configurator. I faked the WIFI id for my card - change that if necessary. I left the MacPro5,1 SMBIOS set for your usage. The rest of the fixes and options - like the audio id and c-state/p-state generation should be correct for all dx58so's. For ethernet, use AppleIntelE1000e.kext. Note that I do not use a patched DSDT - I haven't found a need for one (yet, yes I know I should have one, but Intel motherboards have surprisingly well-written acpi tables, versus some others I have seen) I have rehabman's fakesmc (kudos to him and kozlek,) realtekALC (cloveralc, kudos to toleda,) and appleintele1000e for the intel 82567lm2 gigabit nic onboard (yours may be a slightly different revision, but it works for all of them.) Good luck to you.
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(I know it says 3.07Ghz - just a speedstep quirk, as its at 12x right now)