iMac 27 2019
Can be upgraded to i9-9900kf or i9-9900k
I9-9900kf has better performance.
Can be upgraded from 3.0 base model to 3.7 high end model.
I done it 3 times already.
Remove battery from mother board on 3.0 base model while installing i9-9900kf
After install reinsert battery.