An Audi RS4 is a fantastic car. The main benefits are that it is both very fast and very safe. You are less likely to get into trouble driving it fast than with another car. But it does, of course, demand to be driven fast. Completely barmy (and uncomfortable) to buy one and drive it slowly. If you want a nice, quick 4-door you can drive quickly or slowly, think BMW 335i manual or auto, or a Jag XF 4.2 V8. Or, if you want to go bananas, get a Mercedes C63AMG with the limited slip diff handling kit, an M3 V8 4-door, or a Lexus IS-F.