The Koga Miyata has as long a wheelbase as those bikes and rides great. My old Lotus Odyssey rode quite well.

The Sachs, Surly and International all rode poorly in different ways for me...there wasn't a common denominator. The International was too flexy for my weight and the way i built it (and what I used it for). The Surly transmitted too much vibration, was too heavy and had a weird turning radius. It was a very harsh ride for me, and the bigger issue was that it was IGH, and I don't like IGH.

The Sachs might need some adjustments (I'm hoping that does it). One issue I noticed was that the stem doesn't fully tighten. I can't seem to get it to the point where there is no looseness, and that might be playing with the steering.