Both my best friends have s4s. I have driven them aswell. They are slow compared to an R33, have hardly any torque, but with a few mods they are fast, similar to a modded r33, and get around 160kw atws with exhausts and small boost increase.
Anythin else?
Oh also they are quite reliable if u let them warm up fully before thrashing them. It all depends on the cars history on how reliable they will be... My mates is already leaking oil, had it for 6 months. 60k log books, stock.