You need the V8 for ELSD because the differential doesn't fit on the V6 drivetrain, it has nothing to do with horsepower or torque (so I'm told), it's a mechanical issue.
QTII is more than adequate for "light offroading". It's adequate for a lot of things. It'll happily do its job with a wheel in the air, which is what everyone gets all giddy about and jumps out of the truck to get photos. The ELSD will do it a bit smoother, with a bit less wheel spin.
I think you'd be hard pressed to find someplace that a QTII would get stuck that a QDII would not, and those places are on upper edges of the difficulty scale.
All that said, I got the ELSD, and thus the V8. It was more "in for a penny, in for a pound" kind of thing than any need to be wheeling at "10-10ths" of capability that the ELSD would prevail.
This is the tell tale video that shows the comparison really well. QT2 is quite capable, QD2 has a bit less drama.