Exactly how is crossbow rof effected by bab?

[Tragedian]

I know people have talked about this plenty of times before but it's unclear to me still so I have come to ask a direct question: On an inquisitive using a single crossbow and activating nhb with 15% ranged alacrity gear, inquisitive capstones, and carry on from ld - how big of a difference is there between bab 19 and bab 25? Trying to decide on a multiclass.