Power output dates m5 vs rs6
m5 560hp from 5750-7000rpm, rs6 560hp from 5700-6700
m5 680nm from 1500-5750rpm, rs6 700nm from 1750-5500
the m5 has a wider power band than the rs6 on max hp and max torque output.
rs6 has 20nm more of torque (probably not mesurable)
Despite of Audi saying the new rs6 will be 220 pounds later than hes pescedor we will probably see fully equiped rs6 avant around 2,1 tonnes
(Weighted new S6 was around 2100kg as well, and audi claimes it lighter than the old s6)
So we will see at least 100kg / 220 pound between m5 and rs6 (rs6 heavier)
it could be likely that the rs6 is quicker 0-62 than the m5 due to his all whele drive, but above those speeds i bet for the m5
an unknown parametre is the gear ratio, audi 8 gears vs m5 7 gear..