In manner|lang=en terms the difference between completely and sufficiently
is that
completely is (manner) in a complete manner; fully; totally; utterly while
sufficiently is (manner) in a sufficient manner; enough.
In degree|lang=en terms the difference between completely and sufficiently
is that
completely is (degree) to the fullest extent or degree; totally while
sufficiently is (degree) to a sufficient extent.
As adverbs the difference between completely and sufficiently
is that
completely is (manner) in a complete manner; fully; totally; utterly while
sufficiently is (manner) in a sufficient manner; enough.