Sorry I feel stupid but I am having hard time understanding the rear gears

Lower gear is higher number? 3.08 is high and 3.90 is low?

also just how much change is there in each gear change? I realize transmission and HP affect this but is there a chart to show how much change in performance will occur. For example in my case 400 auto with 250hp motor, with each gear change from the 3.08 now I realize will increase 0-60 time but reduce top end (which is what I am looking for now) SO the move to 3.36 how big a change is that a lot, crazy a lot? How about to 3.55? is the change drastic or minimal? I don't want to change the gears and be like well that doesn't throw my head back?

I'm leaning towards the 3.55 but if someone told me to do 3.73 I would because someday down the road there will me a m21 back in this car, because it is sitting rebuilt in my garage! but if 3.73 wont work for now I can change again!

thanks sorry for my confusion