I don't think it matters that the cars are shaft or belt in mod or even stock for that matter as long as they work well. They end up both being fast and efficient in their own ways so you just have to tune the car torwards each cars strengths.
Man that picture in the rain is wild. They actually race in that stuff in Europe? Scary if they do as it has to be tough on equipment. Looks really wild in that picture that was posted a few posts earlier.