How much gain with lower gears?

As others have said, you wont know anything till you get to the track. If your bracket racing your looking for consistency first.
If your happy with what it runs and its repeatibility, leave it alone.
Change gears, it likely will ET better, how much is guessing at this point.
Remember though, should you change to a steeper gear, you open the possibility of possible traction issues and perhaps tuning changes.
That why street strip cars usually give up something to do one or the other in excellent fashion. Rarely are they great both ways. Just have to figure out whats most important to you