Speed on highway

I ride the '79 KZ1000 shaft...
I hit around 65 mph @ 5k rpms on 5th gear. Is that normal?
I am a complete rookie with bikes, so I don't know.
But sometimes it feels like the bike doesnt display all of its horsepowers
or maybe is it that the KZ doesnt show its colors until I hit higher revs?

Not sure on what gearing the shafties run. but the bike will make decent power at higher revs. but also should be making decent power at 5k.

That sounds about right for stock.
If you have the stock carbs and air box, yeah, it will seem to be a little lean at that speed/RPM's.
Thanks to the EPA and Jimmy Carter and the 55mph national speed limit back then!

Run some Sea Foam or B12 in a tank full of your local high octain gas.
Stock jets are 110s,they might have a little build up internally.
I suggest getting a repair manual for the bike and read thru it.
You will have a better understanding of any 'help' you'll receive here.