I can second that. A pure N/A RS6 would probably find less customerbase than a turboed one. If the new RS6 comes with a N/A with 520hp its unlikely to beat the current M5 (due to weight)...which should be one of the goals (atleast thats what its been over the years).
A N/A RS4 is fine, different customerbase.
I doubt that the new RS6 will weight less than the current one, just look at the old and new RS4 (1620kg -> 1650kg).
I really hope that we get a turboed one, i get too many conflicting reports so i have no idea whats true...guess we gotta wait untill March 07 or something.