I'm new to Zero, but have been riding a while. An FX would be a lot more fun on those Arkansas dirt roads than a DSR, imo.
I went to a Zero dealer thinking I needed the DSR. I did a couple of demo rides on a DS and FX and ended up getting a FX. Like others have said, I assumed the FX and DS would be too underpowered for me looking at the stats, but once I rode them, they both have plenty of power. I'm sure the R models have even more and the SR/F, quite a bit more.
Personally, I wouldn't take a DS off pavement. Bear in mind, I have 3 adventure bikes in the garage and have spent quite a bit of time on them off pavement, including Arkansas and Oklahoma, and compared to them, I wouldn't be happy riding a DS offroad. The suspension is just not there compared to other bikes in the Dual Sport/Adventure market, imo.
On the other hand, the suspension for offroad on the FX is pretty decent stock, imo. It's also a blast to zip around on the pavement as well. Sucks on the highway, but on smaller roads I had a lot more fun riding the FX than the DS. The downside to the FX is range though. Mine can only make about 40 miles on a charge and can only use a 110 plug to charge back up at 9 hours or so.
If I had a 4 mile commute and wanted to play around town and in the dirt on the weekends, the FX is what I'd be looking at. If you like ripping down the highway, maybe one of the R models would be a better option.