The SRW works fine for us towing the Rushmore. I think the long bed helps with stability. No problems with trucks passing in either direction. It tows like a dream, including up and down the Rocky Mountains. Plenty of power going up, and with Engine Brake/Cruise Control/Tow Mode, speed is controlled going down the mountains. We've been in moderate crosswinds. I can feel the wind but it doesn't blow us around. Payload is around 4100, so it handles our pin weight nicely. Our Rushmore has washer/dryer and generator right up front, pushing the pin weight up to around 3500.
If I were getting one of the large toy haulers, I might go for a dually, but I think for the Landmarks, the SRW does the job.