I can't unfortunately, I read it in an Airport Departure lounge when I was waiting for a flight and promptly left it there

It's all because of weight distribution with Audis - they still like flinging the engine and transmission overhanging the front axle which, when you get a heavy V8 involved, means that on the limit the nose will wash wide, slowing it down. You won't notice this in everyday driving - in fact all the way up to about 8/10ths it will grip like a motherf**k*r. But if you intend on any track work the M3 will be you best bet every time.
I noticed evo have lap times for both listed in the back, and they agree with Top Gear that the S4 is around 1s a lap faster, however in the stat that matters, the S4 gets 4/5 and the M3 gets a perfect 5, in fact was their pick of its class (including 911's) from its launch until just recently, when a reworked 911 (the C4S) snatched the title back. But that's a whole other discussion
