Best application to quickly cut video files

Disclaimer: I am a complete novice when it comes to video editing.

The purpose of my videos is mostly documenting motorcycle and snowboarding adventures I occasionally have. So I have lots of footage from a couple of GoPro cameras, but only a tiny fraction of it is of any interest. I tried using iMovie and Final Cut X, and while they aren't half bad when it comes to putting together a whole sequence and adding soundtracks, etc., sometimes I find myself wanting to do a quick "pre-cut" and dump the boring bits to free up space before I have enough time to do a full edit and make something worth sharing.

For example, I may have a 50 min 4GB file that contains 4-5 interesting episodes, each 1-2 minutes long at most. After a week of travelling and shooting I may have a dozen of such files, and it may be a very long time until I have gone through it all and finalized my edit. Is there any way to efficiently cut the interesting sections without any loss of quality and put them away until I get a chance to work with them? Several apps I tried take a huge amount of time to transcode the video, and often end up crashing before successfully saving a slice.