Could you go a numerically lower rear axle and take advantage of the deep first gear?
Yes, but it's complicated. I've been checking into it, and no one makes numerically lower gears for the center section I have anymore. Higher yes, lower no.
Most likely I will just get a newer center section that they still make gears for (I have an open diff so posi would be a nice upgrade while I'm at it), but they want real money for them. ha.
I think the lowest possible is 2.73. I have 3.55 now.