I've been trying dosdude's and foxlet's methods to boot a cMP3,1 with non-standard GPUs into HS beta 2 upgrade 1. In both cases with either an RX460 or a Mac rom flashed HD6870 (both of which work fine under Sierra), the boot process stalls as the GPU drivers load. I rooted out an old Mac HD2600 XT that came in a 2008 MP and put that in after removing the RX460 or HD6870. Result was HS booted up fine (see screen).
And as a final test, I tried using the HD2600 XT as a helper for the RX460 (straight PC card that boots in Sierra but with no efi screen) and got the same spinner towards the end of the boot progress bar. For completeness, I repeated over with the HD2600 XT and the Mac-rom-flashed HD6870 that also works fine in Sierra and saw the same spinner towards the end of the boot progress bar.
Conclusion, the HS GPU drivers are still immature for non-standard GPU cards in the cMP.
With only the HD2600XT installed, the MacPro 3,1 boots straight into HS no problem and everything (BT 4.0 from iMac, USB3, sound, etc.) seems fine.
This is not an APFS install—I'll wait for later betas before playing with that.View attachment 707306
Yep, I suspected that GPU driver could be the culprit by looking at verbose mode login messages, but I didn't have the stock GPU to test as you did.
Good to know that this probably will be fixed in future betas, though.
See ya
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