honey737,
You were right. Captain was wrong. He/She needs to get used to that feeling. However, your later comments are wide of the mark,. 500fpm has its origins in procedural control, and the fact that some systems now use deltaCharlie for display purposes is irrelevant - their origins are in the same place...
Smokie,
'best rate' means... nothing. If I'm flying a long way, my 'best rate' will be ECON. No controller worth their salt should use the phrase. But it does call to mind...
Birdseed 123:
London, good afternoon, Birdseed 123 passing three thousand climbing six thousand Wobun departure, and we can give you a rate you won't believe'
LATCC:
'Birdseed 123 London, you're right, I won't, maintain six thousand on reaching.
Oh, and thanks fourthreethree for giving all the credit to the other bit of sky!!