What is the duration of stay allowed on a Thailand METV and how can it be maximized?

Yes, youll need to leave at least once

You can indeed use a METV every other year for stays up to 179 days. You just can't stay longer than 60 days without either getting a 30 days extension, or without doing a border run for the next 60 days stamp upon re-entry. However if you maximize the stay the METV theoretically makes possible to more than 179 days within a rolling one-year, by exiting and re-entering shortly before the expiry of the visa validity, you might NOT be able to use the METV every other year without raising the eyebrows of Immigration. As long as you use it for yearly holidays of 150-179 days, like for a hibernation, you will be fine. I know people who do exactly that on a METV every other year

If timed correctly then you can squeeze nearer 9 months out of an METV

- Enter 60 days

- Extend 30 days

Leave Thailand

- Enter 60 days

- Extend 30 days

Leave Thailand and enter again right before the 6 months validity finishes and get the last 60 day stamp along with a 30 day extension

You can do 60 days, then a 30.day extension ,then do it at least once more or even two times .

I do it every year for 169 days or so

No. The METV is a 6 month visa which gets you stamped in for 60 days every time you enter Thailand within the 6 months validity.

Do you actually mean the DTV?