I recall (?) default is 400.
Increasing to 1200 can be adverse to other interfaces (it can also be adverse to a single interface).
(Usually the often TAC recommended value of 1200 has only a positive effect.)
Unsure whether a no command will reset to default.
I don't have an actual C9k to confirm initial default value are how to easily restore default value. Do have CML, which might confirm.