I'll be using 100 watts SSB/CW, and have about 75' of twinlead up to
antnenna feedpoint.

You've got me going to do the "system degradation question": I'll run
twinlead to the shack, in spite of the file cabinet.

Now, yes--I can do just fine manually changing my antenna from ladderline
fed to putting it on 160 by jumping both ends together and letting it work
against ground. Long counterpoise in place. Then, putting it back as
twinlead dipole on 80m up.

What's the new question? I normally would go from 160m up through 15m.
If I just used the jump both ends together and feed long wire, which ant
will be better?

Basically, it's whether a long hat vertical would be as good as using my
twinlead as dipole on bands including 80m and up.

I can certainly keep the antenna twinlead fed dipole, no problem. Just
curious.