Hello there. So i have a Mac Pro 2009 (4,1). Some months ago I flashed the EFI to 5.1 for an upgrade. I've installed 2 x 3,46 GHz 6-Core Intel Xeon, an NVIDIA GeForce GTX 1070 8191 MB and 32 GB 1333 MHz DDR3. I've had the 2 x 2.26 4core and NVIDIA GTX 680. Because of Final Cut Pro X 10.4.1 I needed high sierra. So I just did it. There was a problem with the graphics card (macOS graphic drivers where not recognizing the card and I had to use NVIDIA driver). I did the firmware update but I didn't use the patch (the link above). Just the High Sierra installer. Everything is working well so far (I don't know about the wi-fi card cause I ain't got any). The Model Identifier is still 5.1. That was my experience so far. I'm running on macOS High Sierra version 10.13.4 (17E202)