when it comes to cat-back exaust (and any other product that claims big gains) the power gain you will get from any of those exausts are minimal and will not be noticed. the big differences fall into three categories: price, ease of install, and of course exaust tone. IMO some sound better than others, with the Injen and NISMO that sound the best to me. pricewise basically you are paying for the name and bragging rights (just because it is the most expensive exaust it doesn't make it the best). install is easy on those as well and should take no more than an hour, two max. so basically what it comes down to is that if you found an exaust that is the most pleasing to your ears, i say go for it.