Car: 05 Mustang GT, stock engine, no mods.

So now I have a SCT XCal 2 that came with my car. The Xcal2 is uninstalled as I don't have my CAI anymore. I plan on buying a CAI this summer and a 3.73 rear gear.

Question 1: Can the tuner with the XCal 2 change the rear end ratio to make sure I have the correct speed reading?

Question 2: Is there any advantage in getting a SF3 / iTSX over my XCal2 tuningwise? In other word: Is my car going to make more power with a newer tuning tool?

I plan on having only 1 custom tune, so I won't play with all the "features" of the XCal2.

Thanks alot!