Thanks to AMS Performance we have dyno numbers on a Dynojet that show us the difference between the E63, S, and both when tuned. Let's start with a stock 2014 E63 AMG:
Unfortunately AMS did not get torque readings for this run but the car puts out 522 horsepower to the wheels stock. Not bad for a car that is rated at 550 crank horsepower right? AMG is definitely underrating the car a bit.
So what about the S model? Mercedes rates it at an additional 27 horsepower. On the dyno, the E63 AMG S shows 541 wheel horsepower stock. Let's just round it off and say the difference is 20 horsepower at the wheels although without seeing the torque numbers on the standard E63 it is tough to gauge just how much more torque it offers through the curve. Peak horsepower does not tell the whole story here.
However you look at it once both cars are tuned it does not matter if the car is an S or standard E63. They hit roughly the same low 600's to all four wheels power output.
Let's compare this to the rear wheel drive M157 AMG's. The car below is a CLS63 AMG but considering it is the exact same drivetrain as the E63 for our intended use it does not matter. You will remember that before the facelift AMG offered a performance package option which was software that increased the output of the E63/CLS63 AMG.
This overlay showing a non-performance package RWD M157, Performance Package RWD M157, and tuned M157 is courtesy of Renntech:
The E63 and CLS63 before the facelift were below 500 horsepower at the wheels. That means that the base 2014 and up E63 and CLS63 AMG 4Matic models despite sending power to all four wheels are stronger as shown by the ~520 wheel horsepower baseline. Today's standard E63 / CLS63 AMG is about as strong as yesterday's performance package optioned E63 / CLS63 AMG. The AMG S is more powerful just as its crank rating indicates and what is impressive about that is it shows more power at the wheels with 541 stock despite the higher all wheel drive drivetrain losses. Mercedes increased the output quite a bit and built a stout drivetrain to handle it.
You will notice that the tune numbers from Renntech show 583 wheel horsepower and 643 lb-ft of torque at the wheels. Now M157 tunes have evolved since then as the AMS results show and the latest AMS 4Matic tune exceeds the early rear wheel drive M157 tunes. Renntech's tune evolved up to 607 horsepower to the rear wheels:
Weistec is showing roughly the same on 91 octane:
It is interesting to note that despite the higher all wheel drive drivetrain losses the 4Matic cars when tuned are putting down roughly the same wheel horsepower and torque figures as their rear wheel drive counterparts. That should not be the case but it is according to the dyno charts available. Now, in practice, from a roll rear wheel drive M157's have beaten 4Matic M157's. From a stop, 4Matic traction of course favors the 4Matic car despite it being a couple hundred pounds heavier.
The evolution of the M157 and its tuning through rear wheel drive and all wheel drive platforms certainly is interesting to see.