Mine (09 Ultra, also the 08 Ultra) runs fine above 50 in 6th. I stay in 5th if not going over 50 mph in town but if I hit 52, 6th works fine. If I want to accelerate quickly, I definitely down shift to 5th.
Oh yeah, my stereo usually never gets above 1/2 volume either, even at 78 mph on the interstate. The 08 at 3/4 volume.
Now my brothers Softail is a different story, it lugs below 60 in 6th.

 

I can't find 6th gear, so there you go.