RE: So Which is Quicker?
Hey, it's all a matter of perspective. I have modified a few car in my time and typically I buy the mid level package and modify it to what I want. It usually takes more money to do that than just purchasing the higher end model. To turn an R/T into an SRT you'd spend nearly $5k on just the Brembo brakes right there. Now add the suspension, engine hop-ups, after-market interior pieces and before you know it you have spent more to build up your R/T than an SRT would have cost.
If you just want the 6.1, you'll spend somewhere in the neighborhood of $8k and up (I'm guessing, here) for the engine then the labor to install. Does the R/T have the same tranny, shafts and rear-end? I think my SRT was a bargain at $3k under MSRP. Especially since I didn't opt for the Nav and sound system upgrade which will be obsolete in a few months.