It's easy to figure out - if you have stock 2.73's and you want to go to 4.10's, your rpm will increase in direct proportion with the ratio of the gears. 4.10/2.73=1.50. A 50% increase in rpm (HUGE difference). So, if now you're turning over 1600 rpm at 60 mph, then with 4.10's you'll be turning over 50% faster - 2400 rpm. You can use the same math to compare 3.73's, 3.55's, etc. Others may tell you their rpm, but as pointed out above, that can vary from car to car with tranny, tire size, etc. This math will work for your car no matter what size tires you have on it or what type tranny - provided of course that your tach and speedo are accurate.