I want to get the aluminum one but not sure if 4" or 6" would be a better selection. I don't have the max-tow package and truck is levelled on LT285/65R20 tires. I don't think I would ever tow more than 5000lbs but you never know.
The hitch height adjustability range needed is a function of receiver height, trailer ball height, and the sag the trailer induces when hitched to the truck. All of those are unknown.
Generally speaking, a greater range of adjustability is handy to accommodate a range of future / unknown trailer situations.as long as the length does not threaten ground contact.
One alternative if you think you may buy a trailer is to not buy the weigh safe until you have the trailer and can measure its level ball height relative to your receiver.
I bought the Weighsafe Inline 6" drop a few months ago when they were having a sale. It's heavier but it has the same specs as the aluminum models and half the price. It's worked well for me. I love having the adjustability.
I think if I had to do it again I'd get a 8 inch drop as I've used trailers before that have a very low ride height. My truck is the stock ride height with 33" wheels.
I'd say a 6" would be fine for your setup but then again, not all trailers are created equal. That said, I am a huge fan of the Weigh Safe hitch and it's the only hitch I buy. I just like knowing the numbers of stuff so I can properly distribute a loaded weight whether it be a weight distribution hitch or conventional setup and Weigh Safe does that for me.
When I bought mine, I knew I'd be towing a variety of trailers. Some would require a drop hitch but others would need a lift in order to ride level under load. I checked the diagrams on their website and did some measuring to ensure I got a size that would work but also wouldn't allow a lift height that interfere with the tailgate. If it did, I knew it would only be a matter of time until I wasn't thinking about it and dropped the tailgate onto the hitch.