GPU Buyers guide - HD 5870 for High Sierra

Hello, should I get a Sapphire HD 5870? Would patching program get it to work natively in macOS like the official Mac Pro HD 5870s?

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I have a Mac 5770, could I use that to flash?

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Specs: GA Z77-UD3H

CPU: 3570K 4.2-4.4gHz

16GB HyperX

EVGA GTX 570

WD SN550 with PCI riser card(wboot drive for Mavericks)

Intel SSD for mavericks

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My main hang is a GTX 570, that works well in Mavericks, but has a black screen right before the login menu in High Sierra. I boot with iGPU and nv_disable=1.

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I could disable the GTX570, however the HD4000 has similar graphical glitches, with iGPU, than nv_disable=1, and HD4000 seems slow in windows.

The other option would be a Sapphire RX 470, which I'm sure will work with High sierra, however won't work with mavericks unless I keep the GTX 470 in as well. I have 750watt PSU.

Thanks.

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EDIT: Apparently the GTX 570 is part of the problem