I just received two Schwalbe One tubulars, 30mm wide which is the most my Silvio 2.1 can handle. They were $50 each (half off) directly at Schwalbe. Shipping was $10.50 and I got it in four days on a Sunday. I will use Tufo tape to mount them, not the dreadful three-step method with liquid glue.
BTW, for my front wheel I had to file out the fork to make it fit.