Basically , i want to upgrade few 9.X/8.X version DBs to some stable version ( 10.X / 11.X ), At the same time with less down time.
So want to understand whether direct upgrade possible or not between major releases .
From the pg_upgrade documentation:
"pg_upgrade supports upgrades from 8.4.X and later to the current major release of PostgreSQL, including snapshot and beta releases."
You demonstrated knowledge of the two relevant programs that can be used to upgrade and their documentation explicitly states their minimum version limit so I'm not understanding why there is a question. pg_upgrade is the better option for upgrading.