So, have reasonably good success flashing a MSI r7970 Lightning Boost Edition card.
couple of notes.
1. While i have boot screen, as it’s loading, the transition when macOS High Sierra enables the drivers, their is a breif moment when the screen gets slightly glitchy before it loads the desktop, after that everything works just fine. (have yet to test any games though)
2. Out of the two DVI and four Mini-Display ports, I only have two Mini-Display ports that work reliably.
3. This card will NOT work if just two of the six-pin pcie power connectors are plugged in, you have to use the six-pin to eight-pin adapter.
4. Accorfong to the spec’s on the card, it has a max 250W TDP Limit which just puts it over what my cMP can handle but I don’t plan heavy gaming or overclocking. Additionally, this card has a ‘GPU Reactor’ on the underside of it, it’s not needed and can be removed.
Since you flashed the card. I assume you have Windows installed on cMP as well.
If you have no plan to overclock, you may actually downvolt the card to reduce the max power draw. That can also effectively avoid draw too much power from the mini 6pin and trigger the shutdown protection.
The procedure is simple, but can be quite time consuming. Let's assume the default voltage is 1.150V
1) Go to Windows
2) Run some Benchmarks (e.g. Unigine Heaven, the default window mode is good enough.
3) In Wattman or Afterburner, lower the core voltage 10mV, wait few seconds, if nothing happen, another 10mV... (so, start from 1.150V, the next step is 1.140V, then 1.130V....)
4) Until graphic glitches shows up, then raise the voltage 15-20mV (let's say glitches shows at 1.020V, then raise the voltage back to 1.035 - 1.040V)
5) Use this setting to run few more stress test (e.g. OCCT, Furmark), and make sure it can run the whole Unigine Valley, Heaven, and Superposition without any issue. (if unstable, then add 5mV and re-run the stress test)
6) Once confirm stable, use VBE7 to edit the ROM, simply edit the voltage of the highest power state and leave everything as is
7) Save the edited ROM as a new file. And run the patcher to make it a Mac EFI ROM again (VBE7 will disable the EFI part even if you done that before)
8) Flash the new ROM back into the card
And now the card will run at same speed (In fact, sometimes will run faster because no more thermal throttling), but with lower power draw (in the above example, it's about 10% saving, so may decrease the TDP from 250W back to 225W), and run cooler.
I have few 7950, R9 280, R9 380 before, all of them can be downvolted quite a bit. The most ridiculous one is the Sapphire HD7950 Mac Edition card. I can downvolt it from the stock 1.094V to 0.888V but still 100% stable. That's 19% lower. Even my current RX580 can be downvolted to 1000mV. All GPU still running at the stock clock speed, but much much cooler, and lower fan noise.
Another note, 7970 is running at 2.5GT/s
That's expected, and I personally don't recommend anyone do the resistor mod. I did that on my R9 280, and the performance difference is literally zero for all my usage. So, unless you don't mind to damage the card and do it for fun. I see no reason to do that for a general user.
