Can't speak to single portaging as we have never done it.  Have never felt the need.  But have more than 20 trips in a group of two, one as long as 22 days, several were in the 10-12 day range, and have never once thought to describe that condition as "lonely".   ;)

As Mastertangler points out, it is not that hard to make mileage if that is your goal.  Back "in the day" we did that.  We don't anymore, but we could once.