I'm not familiar with the power handling capabilities of the RS4, but I can offer insight as far as sidewinder setups go. First off, to get the most out of brushless you will need to pick up new Nimh packs or go lipo. The 4600 on 2s geared up will break 45 mph and on 3s is capable of highway speeds. The 5700 on 2s won't have the power of the 4600 on 3s, but is still a beast. If you are doing speed runs in a "parking lot" then the 5700 on 2s is enough. The 4600 on 3s will need more room to show its full potential.