Having custom ROM has both good and bad sides. You really can lose some functions or brick your phone if you don`t know what you`re doing. I don`t advice anyone who doesn`t feel confident he can accomplish it to do it, BUT when you succeed you get much better performance and battery life.
After changing my ROM I got 2x+ benchmark score and it goes more than Galaxy S does.
My advice is if you want to change it go to someone you trust knows what he`s doing.