Most affordable GPU better than Radeon 6950

Hello, I’m planning on building a hackintosh with my legacy PC. My 6950 plays games well for me in Windows, but has a coil whine.

It’s ivy bridge with a gigabyte UD5H.

I don’t mind if I downgrade a bit to a HD 5870. If the 5870 is sapphire is there any way to flash it to a Mac version for High Sierra?

I could also maybe get a Sapphire Radeon RX 470. Would that be better?

The build needs to run both High Sierra and Mavericks. I know the 5770 can do this. But that’s a Mac version and I don’t know if flashing a 5870 would work before I buy.