Ancient Aviator
Yes it would be of great interest to hear what the manual performance figures are for the Mk2/Mk3 Chinooks and how they work out in practice. I don't know if there have been any aerodynamic improvements since I last flew the civvy version in 1984. The BV234 manual gave some very optimistic cruise figures. Virtually every takeoff from Aberdeen was at MTOW, 48,500lbs, when the book said the cruise figure might be 135 knots. In practice we accelerated by 'beeping' forward on the cocked hat until the co-pilot (in the max vibration seat) began to look blurred when reducing by a few knots until he came back into focus and stopped complaining produced the initial cruise speed, typically 115 knots.
As regards the Puma I remember one crew claimed to have crossed RAF Topcliffe at 175 knots in a low-level pass one day but on the North Sea I believe 130 knots was typical. Helicopters generally don't seem happy above about 135-140 knots although an S76 would do 145 knots. Judging by those figures, 120 knots would seem to be a very sensible planning speed.
I'm beginning to suspect, as you suggest, that the cloudbase figure above 140 knots is a myth so unquantifiable.
Regards
Boslandew