Leftfield suggestion for you, and probably won’t be quite such a massive performance shock to you.
How about an A4 avant 3.0TDi Quattro. More torque than your RS4, will do 40mpg average, and still plenty bloody rapid. My Dad had an early A5 3.0TDi Quattro with sport pack and it was a rapid motor, and decently economical. Decent enough as the vRS is, it’s a substantial step down from an RS4. The Superb would just feel dull and boring I suspect. Know what you mean about 4×4 though, I never thought I’d use it at all until I owned a car with it, an old A4 quattro. Economy is 10% worse than FWD for sure, but even just for getting out of muddy fields at bike events let alone crappy weather, it was ace! Though tyres make the biggest difference, a set of 19’s with low profile tyres will be useless in crap conditions.
What’s your budget anyhow? New xDrive 3 series Beemer maybe?