I would say a 1600 desert racing is the best way to prepare for class 10 desert racing. A pro buggy on short course is a similar car and has similar power, but is short course racing is so much different than desert racing. Class 1600 is a great class to become a great desert racer in a competitive class. You will learn to race using momentum for the lack of power, learn to drive a car with a narrow track width, and learn from the lack of suspension. The guys that spend a lot of time 1600 racing are often very competitive in whichever class they end up racing later.
Kyle Larsens parents kept him down in the box stock go kart class a long time after most others moved up to 250's . He learned how to be very consistent and win instead of being another overwhelmed kid trying to move up too fast. They got plenty of flack for this plan that surely has worked out pretty well.
Trophy Lite would be a great place to learn as well as 1600.
Yes, class 5 now class 10. I think they are thinking "training" versus "cross-training". I want to start racing more then just my 10 car, but if I am going to, may as well race something that will make me faster in 10 as well. Thanks!