Range wouldn't change that much (compared to Pentastar, not diesel), the HEMI is pretty good at delivering power, and MDS while cruising would make it more efficient running on 4 cyclinder. And for a heavy brick like the Wrangler, when you need HP it could deliver it @ lower RPM where often to go the speed limit against a strong headwind I've often had the Pentstar engine want to jump from ~2K RPM to 4K killing fuel economy. Driving into the wind last month across NFLD and Saskatchewan into 100KM+ headwinds my fuel economy dropped for EVIC quoted (yeah I know it's not super acccurate but shows how much hard engine is working) from 12.1 L/100K to 16.8 , or 19.5MPG to 14.The only way to get a Hemi in a Wrangler is to put it in yourself, unfortunately. On the other hand the range might really suck with a hemi if you don't also increase the size of the gas tank somehow.
This topic has been beaten to death in other threads so I won't waste my time. All I will say is this is not some lightweight Mazda Miata; this is a 3500+ lb brick with large tires.DO NOT underestimate the the 2.0L Turbo. It rips with the 8 speed trans, probably better than the 3.6.