Set up a project to be progressive (you have to do this manually or FCPX will create in interlaced project with the "first drop" media.)
Select the interlaced footage in the Event, go to the Info Inspector and select Settings from the dropdown menu at the bottom left of the inspector column.
In Field Dominance Override, for all things DV (DV, DVCPro, DVD [a.k.a. MPEG2]) etc. set Lower First. For *everything else* set Upper First. FCPX will automatically conform your interlaced video to the progressive format.
Export in ProRes 4444 (the best codec you've got.) Even the "Uncompressed" codecs available are chroma subsampling 4:2:2. ProRes 4444 has 12bit sampling depth as well as 4:4:4 chroma subsampling. (The fourth 4 is for Alpha which you will not need in most cases unless exporting with an alpha channel.)