Not on my machine. I've tried legacy mode for 18 hours straight. No combination would work. I did manage to get it installed, but it wouldn't boot. I finally rearranged my drives so that the original drive was in the original spot. Then did a Winclone restore. It booted twice and ran perfectly. I decided to do a Volume > Volume clone (PCIe/SATA SSD to BAY1/SATA SSD). As soon as I made the transfer, it broke BOTH volumes and no boot condition returns.
I removed each drive and tried each separately but NOJOY!
I have now, repartitioned BAY1 back to HFS+, Reformatted PCIe/SATA0 SSD to FAT and restored the working image again. It went without hiccups but still won't boot. NVRAM resets & SMC resets out the wazoo...
Nothing works now... Just get BONG > White Screen > Black Screen > Monitor Sleeps > Fans on full - NO BOOTING.
Not sure what the problem is. It's a good install, I can access fine with VMWare, but it won't boot.
[doublepost=1529269679][/doublepost]
Looks like a lot of work. I'd like to see a working finish product.
Not sure what's wrong.
But I can share how I did it on my HD7950 (same Mac EFI / driver as the 7970. So, should able to share the same setup process).
I must emphasis that I ONLY did this with the ORIGINAL Win 10 installation disc. The ISO was download directly from MS when Win 10 was just released. That should be the very 1st official release. So, I have no idea if the latest Windows installation ISO can work with the 79xx card (if should, but I never try).
For Legacy installation.
1) MUST use the disc but not any USB installer.
2) Connect a SATA SSD directly to one of the native SATA II ports, not on any PCIe card (It's recommended to remove all other hard drives, but it's not mandatory. Just prevent accidentally format for wrong drive in step 4)
3) Hold C to boot (auto boot to the Win 10 installer)
4) remove all partitions on the target drive
5) re-create a partition with max capacity (the installer should automatically create all other required partitions)
6) continue Windows installation
7) once completed, install bootcamp drivers package (do NOT restart)
If you have any Apple software RAID, perform step 8-10. In my own experience, without these steps, always BSOD on the next boot. And these drivers don't work on the latest Win 10 anyway, so, better to disable them.
8) Navigate to c:\windows\system32\drivers\
9) Rename AppleHFS.sys to AppleHFS.sys.BACKUP
10) Rename AppleMNT.sys to AppleMNT.sys.BACKUP
11) install the latest AMD driver
That's pretty much done. And it work every single time for me.
After this, I will use WinClone to make a backup image file. This is the image for fast "installation".
I never try to boot Windows via any PCIe card. IMO, that's a bad idea. All hard drives on PCIe cards are considered external on the cMP. And Windows doesn't support boot from external drive natively. And cloning from an "external" SSD to an internal SSD seems causing issue in your case.
Once the installation is done. You should be free move the Windows SSD to any native internal ports. But should not move it to any PCIe card.
Also, you should avoid to use any NTFS software in macOS to mount the Windows boot drive. This can also cause a no boot. If you are lucky enough, disable the NTFS mount (only for that drive) may able to resume the Windows bootability.