The Audi S4 (B9) delivers serious performance, luxury, and everyday usability—but is it so good that you don’t even need an RS4? Join me for my first drive as I put this sports sedan to the test!

For its final outing in B9 form, the S4 had both turbocharged petrol V6 and yes, diesel engines. Combined with an eight-speed automatic transmission and the ubiquitous quattro all-wheel drive ...