Any hoo -
I decided to stick in the PCIe card "BCM943602CS Wireless Card Adapter"
Link - that started all of this, into the Mac Pro 5,1, on the basis that some future upgrade to Sonoma or OCLP may sort it. And if it's just sitting there, not working, it should be benign.
In that process, I reset the NVRAM 3 times and the Sonoma install (via OCLP) went all to hell.
The most obvious bad thing was that the monitor now shows everything in Orange and Green, like it's on acid. I tried 2 graphics cards, 3 monitors and now 2 different SSDs. Bloody hell, Orange and Green!
Then I remembered that I'd done the "working" Sonoma install, by installing Ventura and then upgrading OTA to Sonoma, these Orange and Green installs were straight from a Sonoma installer.
So back to year 0.
Luckily I have a Catalina (via DosDude) HDD, I can boot from which works just fine. All the graphics cards and colours and stuff - perfect.
But wait! Sonoma 14.4 and OCLP 1.4 have just been released.
In the blurb in the OCLP 1.3 to 1.4 upgrade, mention was made of a slew of new or updated patches, wifi amongst them. And warnings about various non metal graphics cards - I haven't understood these.
So I'm reinstalling Ventura on the Mac Pro 5,1 with OCLP 1.4, then I'll OTA Sonoma after that.
I do have Sonoma 14.3.1 and OCLP 1.4 working perfectly on my MacBook Pro 10,1. As a "Control", I won't upgrade this to Sonoma 14.4, until I've got the Mac Pro 5,1 working.
Wish me luck...