I am currently running 26 mm Tubular Schwalbe One.
Durability: I am using it for commuting. Schwalbe One definitely is more durable and the ultremos and tubular 4000gp, but still gatorskin is the best for durability.
Ride quality: I like the ultremos better as it seems to be more supple. Schwalbe one feels to have stiffer casing, but the difference is not much. Both feels as fast. For fast cornering though, I feel Schwalbe one is much better than the ultremos. And of course the ride is way better than the gatorskin.
Aeroness/handling: 26 mm schwalbe one seems to big for front. I should have gotten 24 or 22 for front. The handling become really bad when I put 26mm schwalbe one. I had 25 mm gatorskin before I replaced it with schwalbe one.
Mounting: Way way easier than the conti's tubular.
Conclusion: I think it is on par with the GP 4000 tubular. I will buy again due to easiness of mounting, durability, and ride quality. I want a better ride quality than the gatorskin but I don't want to spend 100/tire for veloflex/fmb, and Schwalbe one fits the bill perfectly. I do have to pump tire every morning before commute though