The dell card is identical in every way except for the firmware on the card itself which must be flashed in order to get it working properly.
OPTIONS
I used one of the Dell / Alienware 2GB cards. These can still be got for under $200 on eBay. The Apple card is identical in every way except for the firmware.
This is the Dell / Alienware card here
Grab the Apple ROM file from here: https://www.techpowerup.com/vgabios/?arc... Pay attention to the VRAM size and get the correct file
Prepare the card by removing the Dell metal bracket that the heatsink screws into on the back of the card. You will need to transfer the bracket from the Apple card. Transfer anything else that might be needed.
On the card, with the MXM connector facing downwards and the ATI chip facing you. There are 2 small black chips to the top left of the ATI chip. (one above the other) You need to flash the top one as shown
You will need a way to interface with the chip on the card. I used a Raspberry Pi with a SOIC 8 clip.
Install Flashrom on the rPi. Use the guide here.
https://tomvanveen.eu/flashing-bios-chip...
Connect the rPi, the clip and plug it in. I have my Pi setup as an access point with its own Wifi network. This way, It is portable and can be run of a power bank
scp the file onto the pi. "scp filename pi@ipaddress:/home/pi"
Backup the existing ROM first,
Flash the card and the card works perfectly as a genuine Apple card. I flashed the 1GB VBIOS version first before realising that I had the 2 GB card and had to dismantle the iMac again to reflash the card with the correct ROM. (I repeat, CHECK YOU HAVE THE CORRECT FILE)
After flashing the correct file it should look like this
You will get proper boot screen. No Kext hacking etc. The card works with full acceleration and passes Apple Service Diagnostics
This is indeed also an alternative option out there for us..
But still these AMD chips all die, due to underfill chip design problems..
And with an Nvidia kepler GPU you also get Metal support for Mojave and have a way more reliable GPU in my opinion...
But this is a good option out there for those of use, who still want an EFI bootscreen and don't care about Mojave for example..