FCP 5.1.4 and FCP 6 both use P2 MXF files. (6 is much improved)
...unless you are talking about using Raylight to create QT files to drag and drop directly into the bin. Raylight is not an FCP upgrade, but a separate application available from DVfilm.
Raylight is a $200 PLUGIN that tricks FCP into reading .mxf files without ingesting them (changing the .mxf header into a .mov header). FCP reads the pointer files created by raylight for example: 001AB.MXF.MOV