After you figure out where you are seeking power, google an rpm calculator. Input all your info, then play with the final drive ratio at various speeds. A general example: If want highway gas mileage. You might want to play with the numbers till you hit 2200 rpm at 70 mph. You would get decent mpg at highway speeds, and you would be just barely into your powerband. (Your application could be completely different and my numbers are probably off anyways) A gear provider website like yukon will give you your commonly available final drive ratios. Beyond that, i'd guess someone has tried whatever combo you are thinking, and their review is probably on here.
Tasting a drop isnt going to kill you.
And what doesnt kill you makes you stronger.
Therefore, tasting a drop of antifreeze actually makes you stronger :)
Mac users : control+option+command+8