43 inches, the Wollongong-Melbourne has been done in the past by
B1900 & Dash8-100 a/c. Block time in the B1900 heading south was around
90mins and 75 mins for the return, in those days this was a convenient
service.
The 1900D is capable of 280kts so is similar in speed to the ATR-72 which kicks along at 270kts. The Dash-100 and older 1900s are around 250kt, 20kts over this distance is around 10 minutes so not a great difference.
If the route was viable for a 70 seat aircraft i'm sure QLink would be operating it in the Q400 which cruises at 360kts and over that distance would match the ATR in cost. In fact even Rex would be there as the SAAB cruising at 270kts would be similar sector times to the ATR.