Determining the right regear

Wondering how people decide which regear to go with. I currently have a 3.91, and there are a few options (~4.5, 4.9, 5.2) I see commonly available.

I will be going from the stock tire size to 33s, and that increases my circumference by 7%. Thus, I would want to increase my gear ratio by the same, to recover "factory gearing" (ie so that my RPMS at 70mph will be the same, both before and after the tires+regear):

1.07 x 3.91 = 4.2

So 4.2? That's lower than anything I see available. I guess the other part of the equation is that adding extra weight in the form of larger heavier tires calls for a higher gear ratio, and maybe that's what pushes it from needing a 4.2 to, let's say, 4.5. Total speculation on my part there.

Thoughts?