Thanks for your question. In fact I don’t think Ethereum can and should be used directly in private (despite technically it can) without certain features. This is the reason that Enterprise Ethereum Alliance (EEA) and JP Morgan’s Quorum are what people are looking forward.
Direct comparison between Hyperledger Fabric, Quorum and R3 Corda is something I wish to do, as they are the dominating players in the market and each of which takes a different approach and have the uniqueness. If you wish to take a quick glance on all of them, you can google “Project Ubin” by MAS. In the phase 2 report they have done a practical implementation on all of the three platforms, and some good comments on them.