Road conditions vary. In some countries it's like Europe. In other parts progress is much slower. 250 km/day - as an average, no problem at all, unless you have much rain in Mongolia or mud-slides somewhere in the mountains of Tadjikistan or Kyrgyztan. Of course, you never know about borders. My average distance was about 200 km/day or a bit more and I never had the impression that I had to hurry.