I worked at Altos when the 186 system came out. I porterd a version of the Pick OS to it in 1984 (a solo effort, which was never offered for sale). And I can tell you why it was a slow pig running zenix - the size was made small by removing hardware to a bare minimum, and in the balance the main cpu had to also be the CRT controller - the OS had to sit 2nd seat to the controller, or you wouldn''t see anything.
I have one of the prototypes, and it still works.

I attempted to use the 80186 based Altos many times, but it was a failure from the beginning. It was officially called ACS486.

It''s speed was horrible, and the reliability almost nonexistant. It was a blunder of gigantic proportions.

I bought several at the ''bargain'' price of $4k each, and soon discovered why the great discount - they were junk.

Howver, the other Altoses I''ve used, including ACS8000-10, ACS580, ACS586, ACS2086, ACS1000, and ACS2000, are easily among the best systems in their class.

My OS of choice from the beginning was Oasis8-16/Theos, and it still would be if the Altos was still available.

Altoses running Theos were unbeatable - Xenix/Unix were slow and made for support groups - not efficiency and productivity, where it counts.