llamaman - the VNE for the S61 is 157 kts! Yes fatigue would be an issue but most of that comes from vibration because the Sea King has no vibration absorbers unlike the carson head which has bifilars.
Those that flew the aircraft in that configuration in the US during tests said it was v smooth at 140 kts.
Shenanigans - you are right but the helicopters that are often put forward for SAR are not 'cargo' helicopters they are corporate transport.