Before importing your GoPro CineForm files into Final Cut Pro X, please take into account the following:
1) When setting up your project, its important to set the following options in the FCPX Preferences.
In the 'Playback' pane, uncheck the 'Background render' option.
and in the 'Import pane, uncheck the 'Create optimized media' option.
2) Final Cut Pro X can import CineForm source clips, but the codec is not a native codec and this seems to degrade playback performance. Playback of the timeline with CineForm clips drops frames. The CineForm codec is able to decode to half and quarter resolution, which speeds up playback since the display window is often smaller than the video frame. The CineForm codec is optimized to use integer arithmetic so decoding to a common integer pixel format for display is very fast. Even when the playback window is at less than half of the frame dimensions, the requested frame size is full resolution 1920x1080.
3) Final Cut Pro X caches compressed and uncompressed frames. Compressed frames are read into memory when the timeline is played for the first time. Although this disk read activity seems to execute concurrently with the CineForm decoder, the concurrency is not coordinated in the best possible manner and playback is choppy. Subsequently, when the timeline is played the cached compressed frames are decoded. There may be performance issues when the sequence is large enough to exceed available real memory.
4) Playback occasionally caches decompressed frames so tools that modify the decoding behavior during editing are not synchronized with playback. It is not possible to link to the active clips in CineForm FirstLight for 3D corrections.
5) Cannot use CineForm Intermediate for the complete editing or finishing workflow because cannot export the timeline to CineForm format... although it appears that you can use Compressor to do the CineForm export.