Tony wrote:
So here's the deal. You're at 11,000 feet doing say 120 knots over the
ground and your sea level destination is 100 nm ahead. It's late, ATC
is quiet, very little traffic, CAVU, you're pretty sure centger will
give you whatever you ask for.

What would you ask for?

Your first mistake is to say you're flying a Mooney in your post but
then say your're only doing 120 knots GS. Maybe a super headwind???
That's actually not a trivial question. The answer seen to be that its
controller specific. Certainly if you are IFR you just says "Mooney 94v
would like to start down", or "Mooney 94v, can we get lower" (sometimes
you don't actually know the altitude they can drop you to since that
close to the airport you are often on vectors.) The same if you are in
class B or C.

However, if you are just VFR in class E the answer is "it depends". If
you tell them your going lower about 60% of controllers will say
"You're VFR, why are you telling me this?". If you don't say anything
about 30% will say "please let me know if you are decending". Of course
sometimes you can tell if they are trying to squeeze you into a slot,
but othertimes it just seems to be the controller. This has often
irritated me but VFR procedures are probably at the bottom of the FAA's
list.

-Robert, CFII