So my trusted old nano 1st gen is dying and i need a replacement. Most important task is tracking of running with Nike+iPod. In addition I listen to music. These are the only features I need. Price doesn't matter. So which gen iPod nano should I get? I still see a few 5th gen nanos available in shops. 5th or 6th gen which is best for RUNNING? I don't care for video or any of that.