Congrats on your decision. I am hearing good things about the new S4 and I'm sure the aftermarket support will soon be huge for its new engine.
'13 C63 (LSD, DA, LP) - 421whp (91oct tune only)
'09 E92 DCT M3 (GIAC tuned) - Sold
'13 S4 (GIAC tuned)
'12 E70 X5 35d (Wife's)
'12 E90 335i (Sold) - '10 E92 335i - GIAC Tuned (Sold) - etc...