I have two suggestions:
AUNSOFT (http://www.aunsoft.com/video-converter-mac/) has a video converter which I have bought and used, and it works reasonably quickly and doesn't degrade the image (as far as I can tell, but I'm converting to ProRes 422).
Or: forget about final cut pro x and get Adobe Premiere CS 5 or 5.5, which natively ingests MXF files. Frankly I don't understand Apple's not including a codec to handle the MXF wrapper, but that's the way it is, and Canon doesn't have a converter either, or rather, they have one for the previous edition of FCP, but not this one.