Never had the rs4, but the xray m18 pro was fun. Too much power with brushless combo, still a good 40 minutes with 1400mAh lipo, shaft transmission holding really well to brushless abuse. Even managed to fit a 1:10 servo (don't do that). Too bad I had to trade it.

I think the rs4 shares the same wheels with the m18 non-pro? The ones that you press on that "dishes" and than have a really hard time taking down?