Spec'ing auto vs manual.

Get the brochure on the trans you are considering and look at the ratio spreads between the gears, especially the top two. Know where the engine you are choosing operates with nice balance between efficiency and power, and spec rears accordingly. Having a good spreadsheet that you can plug in all these things, including tire revolutions per mile, and then see what diff ratios get you what you need.

This is why I have a spreadsheet that gives me road speed for the top 6 gears of the trans from 1200 thru 1600 RPM's at 50 RPM increments. I can compare the trans gears with each other and the RPM spread between shifts to find what works well.