A bit out-of-topic post just for the heck of it and for those curious: The fastest record helicopter speed unofficially recorded is 255 knots with the experimental Eurocopter X3 to date but it's a hybrid with twin props to boost forward flight speed (video link):
https://youtu.be/PQNIXxl76qI. Back in the 80s when more TV series became popularized, the viewing public was mesmerized by what Tinseltown put up on the TV screens..among is a super chopper than can fly with the speed of sound (really???)
But those who know something better about traditional rotary wing design and aerodynamics know that isn't possible due to limiting factors like dissymetry of lift and retreating blade stall. At least, 240-Robert and Chopper One were more realistic..and Blue Thunder to some extent..
Now in relation to the thread topic, when the X3 or more better designs become mainstream combining greater speed and hovering capabilities, inspecting something long and undulating like the BWEP pipeline with low-altitude NOE (nap of earth) maneuvers would probably take less than half the time than a traditional helo