Admittidly it sounds bad but I have to say I've had my A4 at an indicated 145 and the further past 120mph I got the more composed and stable it felt. It really was completely effortless. Not saying I would do it myself.

S4 and M3 should be a fairly even match, both are pretty rapid motors. I bet the BMW has better rear leg room though. A4's are shite for that. All my mates laugh and say I own the smallest big car posible