8 3/4 ring gear change for optimum low end performance

If you are really at 1500 at 65, and are willing to run 2000, thats 33% more than your current 3.55. That works out to 4.72. I seriously doubt i would go that far.
In my opinion, going from 3.55 to 3.73 wouldnt be worth the expense, and i wouldnt go all the way to 4.56, so..... chose between 3.91 and 4.11.