"The capability of the current Bell 47 M250 powered STC helicopter speaks for itself"
With a RR300 (250-300), the 47 will not perform as well as a Soloy 47 with a 250-C20B.
The RR300 is rated at 300 HP for take off, 240 HP max continuous . The C20B is rated at 420 HP for take off, 385 HP max continuous.
Altitude performance will suffer. The Soloy 47 can outlift the 206B at 8500 feet.