That's a fantastic road to ride. A Marlin 6 or 7 is surely geared for that surface. And about the washboard.... The only way that washboard surface would be "uncomfortable" to the rider is by riding it fast. The OP's title to this thread mentions that "He Doesn't Want To Shred." That's how I ride. And it's extremely enjoyable. To me.
Compare the Trek Marlin range to the Giant Talon range. My Talon is a 29er and I'll never go back to anything smaller.