Your bottleneck will be your stock catback exhaust. You will not be getting full advantage of the dp you install. There are a few "quiet" or not so loud systems that offer the full 3" piping from downpipe and back. Some tuners like Buschur, will tell you to mod your exhaust system from the rear to front, to start with. More efficient and you will most likely feel the difference.
Research is free so use it. Save your money for a good system for your Evo or at least something that you will be happy with . It's a whole different machine than your old Honda, so think differently with your modding plans.