What load rating should I get for the JKU?
As they say, you should get a winch rated for
at least 1.5x your rig's actual weight. This would mean an 8000-lb winch should suffice. Having some extra capacity "in reserve" never hurts, though.
Is there a material difference between the VR, XD, Zeon, etc models?
Yes!! It is telling that Warn breaks down their winch lineup into three broad categories: Entry Level, Premium Series and Ultimate Performance Series. While they may not tell you every last little internal difference from one series to the next, they do come right out and state that each step up gets you upgraded internal components. This made me really want to buy one of their Ultimate Performance models, but when I went to do so I didn't have the budget for it... so I had to step down to a Premium Series unit instead. I'm still very satisfied, though.
If you want to buy a warn winch, I suggest you carefully study
their web site. They provide you with
lots of important but often-ignored specs, such as pulling capacity by cable layer. Just because two different models are both rated for 8000 pounds, that doesn't mean each one is rated to pull the same weight on every layer. Study these specs carefully, decide what is important to you, and then buy accordingly.
For example, I noticed the Zeon8 is not as strong as the M8000. Sure, they're both rated to tug the same weight on the first layer... but after that, the Zeon trades away weight capacity for line speed. If/when you get to layer four, the Zeon8 is only rated to pull 5189 pounds while the M8000 is rated to pull 6230 pounds. On cable layer 4, the M8000 is still rated to pull 1.5x the weight of my Jeep... but the Zeon8 is not. Personally, I will gladly trade two or three ft/min of line speed for the peace of mind that comes from knowing your winch is not being worked beyond its limits. As for you, well, form your own conclusions.
Synthetic rope is a very desirable luxury, but IMO it is still a luxury. Jeepers around the globe have been using steel cable winches for decades. Especially if you are on a budget, I would suggest buying a stronger winch with steel cable instead of a lesser (read: cheaper) model with synthetic. If synthetic means that much to you, you can always upgrade to it in the future when additional funding becomes available.
Anyway, that is some of the thought process I went through when I bought my winch last June.