Did you put the X5470 into a genuine Mac Pro 3,1? If so, I will add it to the CPU compatibility list.
the Mac Pro 3,1 is an LGA 771 platform not an LGA 775 one. adding LGA775/771 Microcode to a Normal PC AMI or Award BIOS is a fairly easy thing.
https://www.delidded.com/lga-771-xeon-microcode/
its worth mentioning this user does not seem to own a Mac Pro and does not seem to have good understanding of what steppings are...
https://forums.macrumors.com/threads/just-bought-a-2008-mac-pro.2099498/#post-25707626 I recommend reading this post and onwards.
BTW there is even a tool to add microcode to an intel made mobos which is pretty cool (as much like Mac EFIs its pretty much impossible to mod an intel made BIOS) I managed to add Penryn R0 microcode to my DQ965GF to support an E7600 I pulled out of an iMac10,1
http://valid.x86.fr/b2y13x this board does not support this CPU and as such lacks the needed microcode for it, while it POSTs i get no speed stepping (so it would be stuck at 6x multiplier) and I lose a few instruction sets. like SSE4 VT-x and ones needed to boot 64bit windows 8.1+ (BTW since iv added support for a CPU that has SSE4.1 i have been able to boot OS X high sierra on my DQ965GF
)
I managed to do it using the modded checkup7 tool found here
https://www.bios-mods.com/forum/Thread-SOLVED-Xeon-771-Microcodes-for-Intel-775-Motherboard the user by the name of Deathbringer seems to have a lot of know how in BIOS modding and adding CPU support to diffrent BIOS/UEFIs (check out his posts on that forum) I wonder if he could help us add Extra CPU support to Mac Pros and Xserves
(im also wondering if this Checkup7 tool works on Mac Pros but the issue is you have to be booted with the CPU you want to add microcode for. but the Mac Pro 3,1 supposedly wont boot with the E0/R0 CPUs so it becomes catch 22)
