Either the 2011 was a typo, or the Megacab was a typo. A REAL Megacab 1500 only existed in the 3rd gens, and used a 2500 chassis.
With the 4th gens, the biggest limiting factor is rear GAWR - only 3900 lbs. I'm all about pushing the limits, and calling out the OEM ratings that are marketing driven. But axle limits are not a marketing limit, and should be respected.
Power wise, the small block Hemi would keep up / beat any stock big block, with the 8 speed (which the 2011s did not have). When my Hemi is revved out to 5000 - 6000 rpm, my V10 has not chance keeping up.