BOW = Basic Operating Weight
-is the basic weight of the aircraft when ready for operation, including crew but excluding any payload or usable fuel.
What do you mean by "realistic"? The RFM data is factual certified proven data.
Be wary of "additional performance data" which is not approved and clearly says so.
If the aircraft won't achieve the performance in the RFM there is something wrong with it. And I am certain that any customer that found that it didn't would certainly be making a case with the manufacturer and the authorities very smartly.
The 135 I fly "does what it says on the tin."