On my website are formulas that tell you how fast you will be going at a given RPM, or what RPM you will be doing at a given speed. Just plug the values into the formulas and you'll have your answer (it lists gear ratios for MT and AT Zs), so all you need is your tire diameter. A general answer to your question is that you will be turning the engine over faster at a given speed as you shorten the gear ratio (ie. go to a 4.10 or 4.08 from a 3.69). Hope that helps, Mark