I said most of that in my previous post -- that once you reach a certain level the extra cylinders do help make power without breakage.
Fast cars owned by speed shops are a dime a dozen. Name the car and you'll find plenty of fast examples. The Audi vs. Ferrari simply means the Audi is trapping in the 120-123 mph range. Ditch Subaru's weak pistons and you can do the same with an otherwise stock engine with a big enough turbo.
I've built v6's. I've built a 500+whp Supra. My Stealth reached 90 in 7.8 seconds with nothing but a downpipe, MBC, and injectors. That's a 4000lb car with early 1990s technology and turbos so small you could hang one on your keychain, and I did it 7 years ago. A decade newer Audi with fat cash thrown at it should run a tenth or two quicker to 60.
I looked at the S4 before deciding on a new Legacy. I wanted something easier to work on and with the exception of the PITA spark plugs, my car is really easy to mod. With the Green the power delivery is equal to any v6 and if I had a 6spd I'd call it perfect. That won't be optional once power levels go much past 400; I'll then be shopping for a 6spd swap.
Once I have something other than the stock clutch I'll datalog a 0-60 run. Even at only 15 psi I won't have any trouble hitting the 4 second range, and at 22+ it's a certainty.