What’s the most reliable touring bike for long-distance over mixed terrain?

I’m planning a 2,000‑km tour that will hit gravel roads, gravelly sections, and some light singletrack. I want a frame that balances weight and durability, a gear range that handles steep climbs and fast flats, and a mounting layout that lets me carry enough gear without making the bike top-heavy.

Key constraints:

• Total weight (bike + gear) under 30 kg.
• Budget capped at $3,200 (bike + major accessories).
• Need a frame that tolerates 6–8 mm of 20 mm wide tires.
• Comfortable saddle and frame geometry for 8–12‑hour rides.

I’ve looked at Trek 520, Kona Sutra, and Surly Long Haul Trucker, but none of them meet all my criteria. The Trek is too light for my weight and lacks a full suspension; Surly is heavy but has great gear options; Kona is in between but I’ve heard mixed reviews about the headtube height.

I’d like honest opinions on:

1. Which frame best meets the weight/durability trade‑off?
2. How do the different gearing systems (single‑speed, 1x, 3x) compare for long‑distance touring?
3. Any advice on mounting setups that keep the bike balanced while carrying 25–30 kg of gear?

Feel free to counter my assumptions or point me to lesser‑known models that fit the bill. I’m looking for real-world experiences, not just specs.

Thanks for the input!