RS6 comes with an ordinary auto box? I didn't realise this....
The 8 speed is great no doubt, but a car of this caliber needs something sportier.
From my experience of DSG and the ZF 8sp I'd say that there's little to separate them, the DSG might shift quicker but both are that quick that I can't notice the difference and as for the character of each I reckon in sport mode the ZF is even more willing to shift down.
The only negative is I doubt Audi have only the 8th gear as the economy because most likely peak speed is achievable in 6th.