Chrysler lists the AXLE ratios as I had stated above, not the transmission ratios, or even the final drive. My calcs were based only on swapping the axle ratio on the limited for that of the SRT. I'm ignoring the final drive ratios and using shaft speed (assuming 6th gear of the manual is 1:1 for the engine/tranny, as it usually is). I was only trying to get a baseline % of difference if one were to swap the gears in the rears. What you have suggested s is if I were to swap more than that, or compare the two cars. I think the numbers are definitely off, but are close enough for the premise.
I'm still looking, as perhaps I can find an even lower ratio, which would do more for the mileage and 1st gear. (I already start of mostly in 2nd, except for on hills, but there ain't a whole heck of a lot of those in my part of Maryland).