It depends on what you want to spend and how fast you want to go. I have a full Riva stage three kit on my 2006 RXT. That kit has internal as well as external engine improvements and will easily beat any stock ski made to date. That kit was worth it 215 HP up to 295 Hp.I am looking to get some rxp-x modifications. I just want to know what mods are worth it, and which ones i do and dont need.