Well, apparently the Gigabyte Radeon RX Vega 64 Gaming OC 8GB behaves anything then straight.
1.)
@apfelnico 's Vega SSDT did not work at all, not even after careful adaptation. I had to come up with a new SSDT (see attachment) to properly implement all 6 ports (3x DP, 3x HDMI).
View attachment 339958
2.) Yet I was not able to successfully implement a "PP_PhmSoftPowerPlayTable" or "MyRadeonVegaLowFansSpeed.kext" to dominate the fan speed issue (fan always at max. rotation) or to further increase it's performance. In both cases the fans stopped working.
3.) Last but not least, your new VegaGraphicsfixup.kext for 10.14 did not improve the HDMI black screen issue when returning from a powered-off display under PB1. There is also a HDMI and DP black screen issue when returning from system sleep at least under 10.13.6 PB5 and 10.14 PB1 . Also Whatevergreen.kext did no bring any solution..
4.) Finally, also this card has a DP 1.4 3860x1600 pix boot screen resolution problem (VGA only) when connecting to my LG 38UC99-W (DP 1.2 only). Via HDMI, the LG 38UC99-W runs @30 HZ under 10.13. However, 10.14 seems the remove the latter issue (again 60 Hz).
I spent nearly 5 days in trying to fix the individual issues with more or less success.
I finally decided to return the Gigabyte Radeon RX Vega 64 Gaming OC 8GB and go for Sapphire Nitro+ RX Vega 64 implementations on both my X99 and X299 systems. While on X99, the Nitro+ will remain unmodified with it's airflow implementation (3-slot solution), I will water block the Nitro+ for my X299 system (
Bykski Water block from AliExpress).
Now to wait until newly purchased hardware arrives. The Bykski Water block will come from China (7-15 days shipment). The Nitros will arrive within 3-5 days..