I import 720p 60 into fcp x from a camera archive. You can work with it as h.264 or optimize to pro res on import.
it’s Gh2 and af100 footage.
The weirdness is 60p footage exported from FCP 7 as a pro res QT and conformed to 24fps in cinema tools plays slomo in the FCP X event browser but drop it on a 24fps storyline and it plays normal spped.