Thanks for the response to this thread guys.
Shawn, i agree that if you build a better mousetrap the world will beat a path to your door.
Relyon, that is a good practical perspective.
So the hypothetical high speed helicopter should aim for 300-400 miles (with IFR capability), not compromise it's ability to land (and be parked) in tight places. The outlay cost could be marginally higher than a conventional helicopter, and operational cost (per hour) could increase proportionately with speed. Also the payload capacity should not suffer unduly, by allowing some overall weight increase, but we only really need consider up to 250Kts.
Hmmm, difficult spec. Perhaps i should concentrate more on what size of payload would benefit the high speed. The unstated assumption is that the machine should ferry passengers, but would point-to-point cargo be a better approach? Should the machine be sized to suit EMS and SAR requirements?
Does anyone have any thoughts about the size of machine which should be first targeted?