I had both at home and have to disagree with all of your observations. PQ is mostly identical. 5K may have a slight advantage on DVDs but I rarely watch DVDs. Sound, from HDMI bitstreamed, won't have any difference either because that's my receiver's job, not player's.
BD60/605 is slower in loading Java discs than 5k but otherwise it is a better BD player than 5k. Not to mentioned the ability to decode DTS-HD.
One thing to remember for all Panasonic BD players, you have to disable secondary audio in the setup menu in order to get full quality lossless audio out. Otherwise, all audio will be downmixed into lossy DD or DTS.
I only keep my 5K for HD DVD purpose.