As I said before, sadly I can not mod these Quadro vBIOS without cards to test with, it is too easy to brick them. Even with a card it will take many hours of testing for each one, I will try and look at them when I get time.
I don't know why Mojave / Catalina are better at keeping the boot-screen, I did not use DosDudes1's patcher for my Mojave install so it is not related to that. I am still looking into an NVRAM var fix for the bootscreen delay.
I just installed that update and it did not touch my bootrom version, but I have said that before...
Thanks, I am very glad to hear you got it working in the end!
USB 3 power management can cause problems so use USB 2 instead.
On those cheap clips flashing can be slow or fail if the pins are not all level,
if you have problems you must push them in, be careful not to bend anything.
If you only have Windows on SSD you should install the
BootCamp control panel,
after you select the boot drive you will get the instant boot-screen every time,
I would be grateful if you could post a short video of this faster boot time for us?