I took my 4x4 Slash out for the first time today. Theres no need for a Spec class. Open 4x4 will be fine. Out of the box they are so fast that I was/am shocked. The Velineon system, at least in the Slash, screams. I was the fastest thing out there. Any more motor and it would be totally uncontrolable. Seriously, they are everything that Traxxas claimed. I can't believe that they come like that out of the box and are as durable as a 2wd Slash. I pounded the poor thing and it did not break. I was really surprised.