RX 6800 in a Mac Pro 5,1

00:00 Introduction
08:04 The Card
09:55 Installation
12:09 Power
18:20 Geekbench 5 Metal Benchmark Comparison
19:14 Unigine Superposition Benchmark Comparison
21:42 MS Flight Sim Comparison
30:42 Syncretic's VBIOS Fix

Here is a follow-up video showing more information on power draw from this card in a 5,1    • Видео  .

My experience running an AMD RX 6800 Reference card in a Classic Mac Pro.
The RX 6000 series cards don’t work in the 5,1 until the BIOS is fixed with Syncretic’s tool and then flashed onto the card. Lansing McVicker and I have each made videos about this. However, once this is done, they work just like any other compatible card. The RX 6800 and 6800 XT need minimum macOS Big Sur.

Syncretic's VBIOS tool: https://forums.macrumors.com/threads/...

GPU-Z, to see card information and download the VBIOS: https://www.techpowerup.com/download/...

AMDVBFlash, to load the patched BIOS onto the card: https://www.techpowerup.com/download/...

I selected this card for four reasons:
1. Reference card: Two slots thick, so leaves access to the other three slots. I believe this is the most powerful double slot card that can be used in the 5,1on macOS.
2. Power: 250W “Typical Board Power” rating - possibility of running on backplane power and no Pixlas mod.
3. USB: Can the USB port be used for my monitor hub so that my USB 3.0 card can be removed and maybe an nVME drive installed in its slot instead?
4. Performance: The RX 6800 is also significantly more powerful than the RX 6600 XT and any of the previously available most powerful cards like the VII and the RX 5700 XT. Power efficiency is also better on the newer architectures.

Here is a nice review on the 6800 and 6800 XT reference cards:    • AMD Radeon RX 6800 & RX 6800 XT Revie...  

There are long discussions on MacRumors and a blog on House of Moth about the need for Pixlas, and which cards need it. One of the MacProUpgrade group’s experts concluded that cards under 275W should be backplane powered, the idea being that 75W is being provided by the slot, leaving 100W being supplied by each mini 6 pin backplane connector. Testing has shown that the backplane connectors are protected from overcurrent, resulting in a system shutdown at draws over 120W per mini 6 pin. This leaves 20W per mini 6 pin margin for peaks. https://forums.macrumors.com/threads/... https://forums.macrumors.com/threads/...

Others have suggested that the cards pull no more than 40-50W from the slot. Let’s say this card pulls 40W from the slot. To reach this card’s 250W, then, requires 105W from each mini 6 pin. That leaves 15W per mini 6 pin, or 30W total margin for peaks. So, there is a good chance that this card will not overdraw the backplane to the point of a shutdown. There is also the chance that it will. If that happens, then I decide either to sell the card and go back to the RX 6600 XT or go Pixlas.

The House of Moth post focuses on power imbalance caused by cards having one 6 pin and one 8 pin power connection. The card balances its power drawing according to the connector rating, so it will look to pull 2/3 of the power through the 8 pin and 1/3 of the power through the 6 pin. These cards will cause overcurrent of the one side resulting in shutdown, unless a bridge cable arrangement or EVGA power link is used. His point is that shutdowns experienced by users of these cards usually is a result of power imbalance rather than the total power draw. https://thehouseofmoth.com/mac-pro-pi...

Since this card has dual 8 pin power connections, the supply should be balanced between the two cables. If my system ever shuts down due to power, I will come back and update this post.

Update 2/18/2023: Still have had no shutdowns, but on advice from a couple of experts, I added an EVGA PowerLink. Here is a video showing it:    • EVGA PowerLink, RX 6800, Mac Pro 5,1