Oh, please. The S6 as already won in two tests against the M5 never mind the 550i in Germany, ok it might not be as quick but if that's your only agrument then give up. The 335i against the S4 that will be interesting but it has beat the old M3 so if the 335i has the better of the S4 then too the M3. We will have to see if the new one can lay the smack down on the RS4 as you put it, but that will be short lived as the S5 will be out soon.
To say the rwd is the purer driving experience, in what sport? Anytime awd has entered a form of motorsport it has destroyed the competition and been banned, that is apart from rallying which, oh yes is done on roads & forests. Your being suckered into BMW ads if you think 50/50 weight is the holy grail of what makes the pure driving experience, just ask Porsche about that.