Don't have the numbers, but a Boscombe Gazelle on winter trials in Canada in the 70s managed some very high numbers and an unplanned conclusion. :sad:

Drat - rumbled!

Yes, they do go downhill very quickly with even relatively modest pitch angles. I once hosted the senior design engineer for EGPWS from Honeywell, and we took him on a flight in the S-92. One purpose was to show how obstacle warnings could be a nuisance in a high density environment (lots of NUIs) but we also discussed the Mode 1 alerts and the (then) research into improving offshore modes. The Blackpool AS365 accident was still quite fresh in our minds and I tried to explain how quickly things could escalate. But, words can never replace experience so we carried out a series of dives from about 80 kts, with 5 degrees incremental increases in negative pitch. By 25 degrees he really got the message - I think we were hitting 5,000 ft/min in around 6 seconds!

hit 5000 feet down in an AS355F2... in an auto, it comes down like a greased manhole cover...

ZS-Romeo “Inverted” Bravo

To add to the collection of clips showing helicopters rolling and/or looping, this old footage was brought to my attention:

Sikorsky CH-53A conducting rolls and loops over Long Island Sound in a joint Naval Air Systems Command and Sikorsky trial in 1968:

https://www.facebook.com/reel/1237402674817234

(I hope the Facebook link is retained)

Wow, seeing a big helicopter like a CH53 doing this is impressive, thanks for sharing the link.
TEM must have not included "lets do this at an altitude where we have some margin, just in case"
(Starting the loop @ 1150ft and ending it @ 920ft)

Some interesting (and amusing) background to one of the pilots involved:

https://www.popasmoke.com/ed-creamer/rpg/