Was convinced that i saw just under 80% once when I was starting my PPL(H). One closing the throttle for a practice auto, I pulled collective instead of dumping it. Luckily my Instructor was lightning quick and covering the controls and he recovered it. I swore i saw just under the 80 (I was positive it was more like 75%) and he swore it was 80% because 75% wouldn't have been recoverable. Not that I care now, just that i wouldn't ever go there again.
In an S76 sim once, I had a dual engine failure and some other problem (cant remember what now) but I pushed right pedal, the collective came up, the Nr decayed and I watched as the blades stalled in front of me. Next stop? The ground, nose down, a sudden stop and a red screen. Very unpleasant even though I was just being shown something, but all the same something you really need to be aware of especially in low inertia rotor heads.
Look at the other thread on flying low level in bad vis, you slow down, then slow down some more, then you forget carb heat, the air is moist, you're at partial throttle, hmmm, not a good place to be.