If you want a lot more usable torque then you should get rid of your heavy stock x-pipe and swap for a titanium catless unit. Should run around $1,500 installed. Car will be lighter by ~ 50 lbs and you will gain 20-30 lb ft of torque throughout the entire rev range.
Daily: 2013 e92 M3 MW FR DCT ZCP / ESS VT2 650 S/C, MRF mid/Akra slip, ST BBK
Track/Airstrip: 2011 997.2 Turbo S PDK / GIAC tuned / Ohlins coils+LCAs+endlinks setup by BBI Autosport
Beater: 2013 X5 3.5sport