When importing r3 footy directly into imovie the 60fps is lost becuase it cuts up the footage into 30 fps shots ( losing quality when it comes to slo mo). To use the go pros full potential you can follow these easy steps.
1) download JES Deinterlacer for free http://www.xs4all.nl/~jeschot/home.html
2) import your video inth JES
3) click the project tab and change the video speed accordingly
4) export to desktop
5) import to imovie
This is how I learned it
These are my results...
Hope this helps someone out..
Happy Editing NS