In 2012 and 2013, as a Gold I usually always booked standard rooms and got upgraded to Exec Level at these properties: Budapest, Budapest Westend, Mainz, London Tower Bridge, London Canary Wharf, London Doubletree Westend, Birmingham (UK) Metropole, Dresden, Rome Airport

Copenhagen Airport was strict in allowing only one category upgrade (admittingly to a very nice and newly refurbished Deluxe Room).

Cavalieri Rome I was lucky to get an upgrade to a fantastic view of Rome on 5th floor.

Brussels City (booked via opaque channel) - Upgrade to Deluxe (very spacious and fairly modern decor) / no exec level in-house

Malmo (now no longer a Hilton) upgraded me to a large corner room with drink vouchers (no exec level in-house).

London Docklands upgrade to River View large corner room (again, no exec level in-house).

at a number of properties I stayed multiple times with same treatment.

Overall, I have been treated very well as a Gold (this above list of properties is exhaustive i.e. no other stays at Hiltons), denied Exec level (where available) only once.

I usually don't contact the hotel before, and most of the stays were paid stays (except Mainz, and Points&Cash for CPH).