Adobe Premier Elements 10 is my favorite for the files from my Panasonic SDT-750 that records the same type of files as yours.
Don't get put off by the marketing that says it will do cute, themed automatic video. Below the surface are more amazing tools than I thought possible for around $65. In fact, looking around the internet, you may find comments that there may be few reasons to buy the $600 Premier Pro, unless you are trying to manage multiple cameras on live feeds or 3D.
For sound, it will handle up to 99 separate audio tracks with full control using mixers, filters and effects.
To speed up or slow down a clip, there is a "time" tool that you use to grab the one end of the clip and shrink or stretch it to whatever you want.
1080p60 files do not cause me any trouble. They read into PE10 without issue. So far, I have not found how to make it render to 1080p. Instead, it has a slew of presets for creating optimized files for everything you might want to do from disks, media players and YouTube.
(On edit: I figured out how to render to 1080p60. It was easy but not obvious. In the share mode you pick an MPEG4 preset, select "Advanced" and select the 59.94 frame rate.)
You can download a full trial copy and there is great online training at lynda.com that will get you going quickly with the finer points of audio and video control. Go there and watch a couple of free lessons and you should get an idea of how it works.
I am enjoying learning and using it alot!