One thing to consider is whether or not you rely on tire air volume to help in obtaining a softer ride, like on the 2400. The more fluid you install the less air you have to compress when you hit a bump. On a small tractor weighing 1800# and a pair of 3200# rated rears which come standard, getting a soft ride is tough.
I put fluid in my tires at first but found that running at 10 psig, the fluid was instrumental in having the tires come off the rims in normal (bumpy) field use. Going back to full air fill and using wheel weights for the added weight worked much better.
I have just over the axle fill in my 6530 only because it's the contents of a 55 gallon drum that the tire guy had in the back of his truck; one drum per rear tire. It has served my purposes.