On a triple trailer the 7000 pound axle upgrade is just over $200.00. The goodyear tires are a little over 2,000. I think you can buy the tires at a local tire store for that and save the stock tires to put back on when you sell the rig or get a trade from the tire dealer.
My 3800 is to be built in 10 days. I was told the 7000 pound axles do not increase the gross vehicle weight of the trailer. If so what is he advantage of getting them? I am getting the stock tires and if we see a problem will upgrade at a local tire store.
AT $200 I wouldn't hesitate at getting the 7K over the 6K.
At $2000 for six GY 614's a key point is what wheels are currently equipped from the factory?
If they are the standard wheels used in years past, you cannot mount GY G614's, or any 110 PSI tire. Previous rims were rated for only 80PSI.
In that case, the $2000 for the factory upgrade will be significantly less then the aftermarket price of tires AND wheels.
If you can't physically check the wheels, a "non-scientific" method is to count the spokes. 5 spokes are 80 psi, 8 spokes are 110 psi (typically).