Well, i don't have an RS4, but all 1:10 touring cars are pretty much the same. Anyhoo, I run an OFNA 1:10 RTR box with two 550 motors. It's a nice box, but the motors aren't the greatest.
You know, if you're shopping for a new box, i'd highly recommend getting a 1:8 scale box. They've got a better motor in it with much more torque than the 1:10 scale starter boxes. In hindsight, i probably should have gotten a 1:8 scale starter box.
But on a sidenote, if you get a 1:10 box, if you upgrade the motors to aftermarket ones, you shouldn't have any trouble turning over any motor. But the stock motors really aren't that good.