Level is clearly a relative term here, the Sea King doesn't hover level, it is usually about 4 to 5 degrees nose up - but compare that with 8 to 10 degrees nose up of the 139!
However, the Sea King(or similarly shaped helo) could be capable of 140 kts plus with the right upgrades.
The S-92 is the closest thing to a bespoke SAR helo at the moment although much of the R and D appears to have been absorbed into the Canadian Cyclone contract. That seems to have a pretty good mix of straight line speed and sensible cabin size so it is not impossible.