No luck using Radeon HD 7750. Went back to my Radeon HD 6670 for now.
Installed to my Intel 320 SSD. Had issues using APFS, after install I had kernel crash. Backtrace crash similar to some others mentioned. Safe booted, deleted all old kexts from system, rebooted using Rehabman's Clover fork r4210 and -f.
Issues: after upgrade, no login screen, just mouse pointer and black background. Followed some advice online and
rm -f /Library/Preferences/com.apple.loginwindow.plist
rm -f /var/db/.AppleUpgrade
(single user mode obviously)
That got it working but it didn't seem stable. System crashed and beachballed a bit. Maybe I did something wrong, or had incompatible programs (not clean install, upgrade).
So, installed to my SSD using USB adapter which kept HFS+. Installed using Mac Pro 6,1 smbios, then went back to 5,1 again (not sure if 6,1 is needed anymore, installer didn't warn about firmware upgrade).
Issues: after upgrade, again no login screen, just mouse pointer and black background. Followed advice online and
rm -f /Library/Preferences/com.apple.loginwindow.plist (backed it up first)
rm -f /var/db/.AppleUpgrade
Logged in, restored loginwindow.plist, reinstalled sound using command130 from Realtek AppleHDA-thread.
System now seems stable, will evaluate for a week or two and then decide to keep High Sierra or return temporarily to Sierra. Will not use APFS until more stable (and I see little use of it at the moment)