If you replace the resonator with a straight pipe you will get a drone at 3500rpm that will rattle your fillings loose leave it stock or install a rear exhaust. The best bang for the buck mod I did to my old 05 GTX 185 was an external intercooler, picked up about 3 to 4 mph with a prop repitch and the throttle response was noticeably better.
[video=youtube_share;R2mZvhkk_To]https://youtu.be/R2mZvhkk_To[/video]