Hi I have posted something similar on another thread but thought it might be worth posting here.
I read that i does not matter that we can set Sequence Settings in X because once we output from FCPX it points but to the original media.
So...if that is the case why bother to do anything other than import and create Proxy Media in the first instance when we import Media.
Then workflow would be "Create Proxy Media" and use appropriate ("Use Proxy Media") playback settings in preferences and then before export change playback setting to "Use Original or Optimised Media" (we would be using original because we have not transcoded to Optimised...just Proxy) and then in project properties change render format to Pro Res HQ or 4444.
Then render it out (or not bother because it will do this when it exports anyway?)
Then export because FCPX will import the original native files when we create Proxy Media anyway.
If this workflow makes sense it does make the notion of "Create Optimised Media" when importing media completely redundant.