Sorry to Necropost but yes, even my 9600k with iMac19,1 doesn't throttle to 0,8. With iMacPro1,1 all the states are up and running well... Even my rx590 behaves sensibly better, with less power drain and idle clocks. Strange right?
EDIT: It seems that the iMac19,1 SMBIOS has no problem now...