Can a flashed Mac Pro 2009 (5,1) support macOS Mojave

Can macOS Mojave be installed on a Mac Pro 2009 that has been flashed/upgraded to the 5,1 firmware (Mine already is) with a Metal supported GPU like a AMD RX 580?

Yes, got Mojave on my 2009 5,1 flashed with the High Sierra update this morning using the 6/18 Mojave download.

The Apple store wouldn't let me download Mojave directly to my 2009, had to download on another machine (a 10.13 Fusion VM) then create a bootable USB, boot my 2009 from the USB and install from there.

Yes, per the specifications macOS Mojave runs on a Mac Pro 2010 with a Metal-capable GPU. The software is unaware that your machine is really a 2009, as it only checks the board ID which matches a 5,1 machine. Currently running Beta 5 on my 2009, with an AMD Radeon R9 270X flashed with EFI firmware. Be sure to remove any other GPUs from the machine. I first had an issue then remembered I had my original GT 120 installed. I was required to update my EFI firmware, and it successfully updated to MP51.0089.B00. The firmware update may require a GPU with EFI firmware (gray boot screen.)

just nervously updated from High Sierra to Mojave on my Mac Pro early 2009 (4,1 flashed to 5,1. - dosdude patch for High Sierra ages ago - then the Mojave boot installer/patcher usb drive method by dosdude just last night..)

it did feel a bit like an impulsive move from what i'd read about compatible systems, i was expecting maybe a complete death of the factory fitted gpu as its not Metal (still using the original nvidia GeForce GT120!), was ready to buy an new gpu.

so theres hope out there, not experienced any major gpu issues other than a lack of transparent dock and a few other minor things, but still does dark mode.

TBH just relieved it actually booted. however i'm ready to go for a new rx560 if needed....

good luck out there anyone searching for answers.

Interestingly, My Mac Pro 4,1 flashed to a 5,1 had no problem downloading the Beta for Mojave (7/27/18), but will not do the firmware update.

It's not clear to me hw it's failing as my video card is a modern nVidia that doesn't show the great screen at POST.

I think I will try to replace it with the original card and see if I get any more info that way...

Much later I add... using the original card (Radeon 5870) I was able to install the firmware update and then swap in a modern video card.

My nVidia 1060 card still isn't usable, as there aren't web drivers for Mojave yet, my RX 580 works but doesn't provide audio over HDMI, which was flawless in High Sierra.

My early 2009 4.1 flashed to 5.1 installed the firmware update and installed fine. I hadn't read about Metal GPU requirements, and my GTX 970 didn't work (grey bars at top of safari, etc.)

I switched it for a gtx 680 but it's very flaky. I'm trying to edit video in Final Cut, Premiere and DaVinci Resolve, all of which crash regularly and quite spectacularly.

Going to try an RX 580 next...