Within the London TMA if you didn't utilise the a/c abilities, and the pilot's of course, NOTHING would move.
I'll have to take your word for that, never having been to LTCC, but I've met Paul Upton from there, so he can tell you what our centre looks like.
It is considered poor technique in Oz. Even by our busiest controllers in TMA. As for best rate meaning anything other than climb like a banshee (or a fart in a bath), well I don't know what pilot would think that best rate means for economy especially when you say "due traffic".
BTW, didn't we have this"expedite" argument in another thread?