For towing the weight your talking about either gears should be fine. If towing really heavy I'd want the lowest I could get.
A longer wheel base will tow and ride better than a shorter wheel base.
The reason for the lower GVWR packages is to get around certain DOT laws that kick in for GVWR over 10,000 pounds. If you're not using the truck for commercial purposes most of them shouldn't apply anyway so I'd just stick with the 11,400 GVWR package.
That's one of those things that makes it a little funny that some people get so bent out of shape about loading over the GVWR. My work truck is a Chevy 3500 which normally comes with an 11,500 GVWR but my boss ordered it with a 10,000 rating to avoid some DOT requirements. The truck is the same, it hauls 11,500 just fine.
