YES....and no. You need to be more concerned with it when you start loading the trailer down. Look at the tongue weight. Generally it's between 10-15% of the TT weight. 5% of 8500 lbs will be substantial when you are already close to the max of your capabilities. For the sake of argument, let’s say that that tongue weight will end up on your TV axles (some will contend that some of it is projected back to the trailer axles with a WDH). However, how the trailer is loaded will GREATLY affect where that weight is projected when the WDH is in play. In other words, tongue weight is needed. But, the more you have on any given trailer the more you will be projecting onto your tow vehicle. I wouldn't worry about it too much, but just keep it in the back of your mind
This is what several other posters are getting at. You will most likely exceed any one or both of those axle numbers long before you exceed your tow rating. For me, I am usually closer to exceeding my max in the front axle more than the rear.
My SUV has a much shorter wheelbase with a tightly adjusted WDH when compared to most pickups.
Whenever you get your trailer, make sure you get some real scale time. Since your intention is to get the largest trailer that you can comfortably and safely tow, you will most definitely be flirting with overloading some rating somewhere. The best thing is to KNOW where it is, and make adjustments accordingly. There are too many options in which to load a trailer and WDH adjustments to accurately guess where your weight is.
It took hitting scales a second time before I started to get an idea of how loading my trailer affected my TV.
For instance, my FW tank is just behind my first of two TT axles. So its center of gravity is behind both axles. When I initially weighed my trailer with all holding tanks empty I was just fine on all of my specs. Two seasons of accumulating stuff here and shedding stuff there plus the boon docking trips where I would travel with a full FW tank gave me a false sense of security as I had already "been to the scales".
Only after I added a truck tool box to the front of my TT and filled them with a couple of deep cycle batteries, did I start to wonder about my specs. So just before I went on our annual Memorial Day boon docking trip last month, I decided to hit a scale. I went the night before we departed, so the trailer was accurately loaded as it would have been for a trip. I found that I was so concerned about the effect the batteries and tool box would have on the tongue (plus I had a pair of CPE gensets in the front pass through storage) that I wasn't worried about the food in the fridge, the food in the pantry, booze in the coolers, and water in the holding tank (all behind the tandem axles). The scales showed me two things, my 800 lb. WDH spring bars were overloaded by 150 lbs. But more astonishing, the added rear weight of the trailer kept the tongue in its same relative position. This in turned simply pushed most of that weight to the front axles. I was less than 50 pounds from my overloading my front. I dare say that the DW weighs more than that. So I knew that the 300 mi I had planned on driving the next day were going to be overloaded miles.
So after changing the spring bars out ( I had ordered the 1200lb bars on accident that proved to work out) , readjusting the WDH to the new bars and moving some cargo to the front of the TT, I was able to take well over 100lbs from the front axle, redistribute it to the rear axle and TT. It cost me a good $ 30 in scale fees, but few can argue that I wasted my money.
I was sure that I was tongue heavy, as I thought that the position of the FW tank was too close to the tandems to make any real difference in weight bias. You couldn't have convinced me otherwise without the use of that scale.
All of that being said, you have the benefit of a much longer wheelbase when compared to a SUV. It shouldn't be as twitchy as the longer wheelbase gives you more leverage.
I hope that this doesn’t do more to confuse you than it does to help you. I am just trying to share what I have learned to give you an idea of things to consider.
Edit: Inaccurate numbers.... remedied after referring to weight slips
