The RS4 3SS is very fast if you mean straight line speed, its easy to work with also very durable and parts are easy to get. There are many factory and aftermarket hopups as well. The engine from the SS is pretty strong already, but if you want a faster engine, any new .12 .15 and .18 (.12 based) engines with Rotary carb (also check the crack shaft) should fit into the car. However, IF you do plan to join any race, the R40 will be a much better choice since its a race purpose designed with optimised performance and handling. You can also choose higher performance engines (such as Novarossi, RB, etc). You should check the R40 thread for MUCH more details. And any 200mm body will fit these cars. Hope this helps and good luck!