Emratty, MW, and all..
I think the point about speed is that if you're asked, do it. If you can't, be it because you're too heavy or too light, TELL THEM! And, TELL THEM EARLY!
The response to a quick "I need 170" (eg heavy 777-300) or "I need 140" (light 330) is usually "approved!", followed by a tighter or wider radar vector. Not a problem if they know early enough.
If the pattern is full and I can hear everyone else is getting 160 from 15 miles, I speak up, tell them I'll need 170, take the 20 sec radar vector penalty and not have to have gear and landing flaps out from 15 miles. (or more)
