Hilton writes:

I have a question from a friend. Her daughters have nut allergies. She
wants to know how long it takes from cruise (41K?) to a gate from the time
they notify the crew of a medical emergency (e.g. anaphylactic shock).
Obviously it depends on their proximity to a suitable airport, but I'd like
to hear from the airline pilots in this group. She is specifically
referring to a flight from the SF Bay Area to the NY area.

At least 30-40 minutes. If she is indeed prone to anaphylactic shock, she'll
need to be treated on board. And there may not be any airport with suitably
elaborate treatment services available within a short distance. If it happens
over the Rockies, it's going to be a lot longer.

As a pilot, what kind of descent rates can a 737/A320/747 etc get in a
medical mergency?

The same rate it can get in a non-emergency. The structural limits of the
aircraft do not change in emergencies. The kinetic energy represented by high
altitude and high speed must be dissipated in every case.

Would this descent rate be different than a descent for decompression?

No.

While the crew of the flight may make every effort to expedite the landing of
the aircraft at a suitable airport should that be deemed necessary, that
effort will not extend to endangering the flight, crew, and passengers. If a
choice must be made between endangering the entire flight and delaying landing
to treat your friend's daughters, her daughters will lose. If your friend
imagines the pilots putting the aircraft into a wild dive to get to an
airport, she has been watching too many movies.

In every case, the emphasis must be on emergency treatment while in the air.
That's why many aircraft must carry defibrillators now.