Once you're done with all your mods, check your A/F mixture. I will bet the stock ECU will run a bit lean. If you go with high flow cats and and exhaust, the drop in back pressure will actually make your ECU will compensate and you will feel your car is actually slower. Let technosquare re-flash your ECU. Then you will really see what all your mods have done to your car. The difference is a no brainer.

 

with just a plenum spacer, the performance gain will be negligible