The big difference I saw when comparing the specs of both is the warranty. The Terra is Lifetime while the AT is 2 years limited. As far as I am concerned, a winch is alway strong enough until you really need it, then you realize you might wanted something a bit stronger.... Go big. I have a Warn 4500 on my P5.... The 3500 would not pull my P5 mounted on track out of the snow so I had to replace it with a 4500....
You have to realize that you loose power for every layer of rope there is on the spooler. Here are specs from WARN for a 3500
View attachment 18996
So when your winch spool if full of rope, a 3500 pds winch can only pull 1535pds
Here are the specs for the 4000...
View attachment 18997
There is 836 Pds difference between the 2 when the spoolers are full.
It all depends on what your needs are...
Hope this helped you and did not confuse you more...
Mart!