First off,
If you put in a 4.11, in 1st gear at 600 RPM, you would be doing something like 3 MPH. The higher the ratio, the lower the gearing. I think if you added the speed booster and the SRT rear-end gears, you would get what you are after, as you can stay in 1st longer and really squeeze out the power of the engine, and have more speed when you do shift.

Since I use my Limited as a highway cruiser, I was looking for better mileage and more efficient shift points. I did some calcs, and by swapping the rear end in a limited/base for that of an SRT-6, you would pretty much change things by 6%, across the board. The limited has a ratio of 3.25:1, and the SRT-6 is 3.07:1 (source-Chrysler website). At 70 MPH, we get 2,591.186 RPMs of the engine for the Limited, and 2447.647 on the SRT. 5.9% difference. (using the 29.5" Tire diameter of the Continental ASP Tires).

If we use a standard RPM of 2,500, with the Limited we get 769.2 rotations per minute of the tire, and 814.3 for the SRT. Again, 5.9% difference. The Conti rear tire requires 801 revolutions to travel 1 mile, so the SRT will go 1.016 miles per minute at 2,500 RPMs, and the Limited/Base at .960 miles per minute. SRT will be traveling at 60.96 MPH, and the Limited/Base at 57.6 MPH. If at that speed in a limited, we are hypothetically getting 30 MPG, the swap will result in getting 31.77 MPG.

If we got 350 miles per tank before the swap, after the swap, we would get 370.65 now. At 350, with 30 MPG, we burn 11.67 gallons of gas, and at $2.50 a gallon, thats $29.175. Modified, we burn 11.02 gallons, and at $2.50 a gallon, thats $27.55. A savings of a whopping $1.63.

Hardly seems worth it, being that it would probably cost in excess of $500 to do.

I went to public school , and TWO public colleges so please correct my math if in error.