The first race is RS6 versus RS4 and the RS4 predictably is destroyed. It isn't even close. It feels like an eternity by the time the RS4 crosses the finish line after the RS6. It's a 2 second difference.
The GT-R race is the interesting one and it is the more worthy competitor in a straightline contest. The GT-R being lighter and also having all wheel drive gets out of the hole quicker versus the RS6. It increases the lead as the race goes and convincingly beats the RS6 down. It's lighter, it has a dual clutch trans as opposed to an automatic, and is simply faster.
The RS4 does the 0-1000 meter sprint in 24.06 @ 135.4 MPH. The RS6 in 22.04 @ 146.9 MPH, much faster. The GT-R? 21.29 @ 151.4 MPH. So while it is quicker and faster the RS6 is pretty close and certainly impressive for a wagon. The lighter RS7 should make things between the two more interesting and closer. Regardless, the new RS6 is a strong car even though it does not really improve on the previous generation's twin turbo V10.