S4 or RS4 not sure
 

I have an S4 2012 prestige pack with 7 speed. I am debating getting an RS4 instead. I bought my car last year and within a week I had APR basically do everything they could to it. Also upgraded rotors and pads. Put about 12-13k to make it how I wanted. Only thing else they can do is cat back exhaust which only adds a couple hp. Basically I am maxed out they said. Quick list of what I changed but probably forgetting some stuff
Ultra charger kit
Cold air intake
Under drive pulley
Power stop pads and rotors
Down pipes to remove cats
Transmission tuned
Engine tuned 93
Bigger supercharger pulley
APR supercharger cooling system
Plus more I know I'm forgetting.

So obviously I am not interested in buying the car brand new. I would void the warranty within a week. I have 3 kids all 9 and under so they fit just fine in the back. I was planning to get the RS7 until I realized it has no middle seat in the back. That was not a smart on their part. Anyway I am looking at newer s4 and RS4. I don't mind spending 15k to make the car like I want. I will buy a year or two old for those reasons. Plus gives them time to fix any bugs before I buy. Inside they look pretty identical in size. What are the potentials for each and why would you pick one or the other? Got money to play with on upgrades so I am wondering if the s4 can be made to make more power the RS4 with aftermarket