Cant speak for the 600 as I have only flown one once. The 500 in high speed flight auto rotates like a dream in fact you have to use a different technique than that you are normally taught.
Remember this is high speed flight ( above 100kts ) Say one is cruising at around 120 to 130 kts. If you close the throttle the first reaction should be to haul the cylic back leaving the collective lever where it is. The effect will be initially for the aircraft to climb at about 500 ft a min for about 5 to 10 seconds. You are aiming to get the speed back to 80 kts ( range speed) If you put lever down first the nose will drop severely causing one to yank the lever back up to protect Nr.
Once you are at 80 its then control the speed with the collective i.e. by lowering it slowly the nose will drop which means you can apply rear cyclic which increases Nr and gets the speed back to 60 kts which is best auto speed.
If you bottom lever at 130 its you will have ac on its nose with about 40 to 60 degrees pitch down. Effect is then to haul back cyclic which very very rapidly increases Nr so you have to rapidly bring lever back up.
Now if you have not been taught this technique then a 600 which I am sure flies in a similar manner ( but with higher ROD ) but faster then a 500 I can see why you would chop you boom off by bottoming lever with a rapid rear cyclic to stop massive nose drop !