Few points:
- If the trailer's light enough, you may not ever get stuck with a 4x2. We didn't with our 4K trailer, but did several times when we upgraded the trailer to 8-8.5K bumper pull. With a 10K bumper pull I would want 4x4 and all-terrain tires if ever going off pavement onto damp ground, wet grass and so on.
- But we had Highway tires on that 4x2, Michelin MS/2, really poor off-pavement tires. Perhaps a 4x2 with All-Terrains would have been good enough? Dunno. But recall one situation where the truck's front wheels were on pavement, and the rear wheels were digging into sand while pushing the trailer back up a hill. ANY front wheel traction would have been nice there.
- Coming from the North I used to think snow/ice were the main reason for 4x4. Not so when towing heavy. Learned that lesson the hard way.