[Test-Equipment] Fluke 8500A series: which one?

[Gottfried Ira]

Hello,

used 8500A, 8502A, 8505A and 8506A DMMs are available at very
affordable prices. They offer 6,5 digits resolution
and can be equipped with IEEE, TRMS, Ohms and current shunt
options. And they look all the same!
But that is all information I could gather.
(www.fluke.com has an archive of obsolete equipment, but
does not list the 850xA.)

Does anybody know the differences? Should a certain
model be avoided? What would be the optimum for
a nice home lab?

Any hint appreciated!
Thanks,
    Gottfried