Performance wise, unless you are bumping 500 horse you dont need a 5" system. Some guys like the sound of a 5" system but on a performance level you can get just as many ponies through a 4" system. EGT's wont be much different between the two either. 5" systems are pretty much ego factors.
Welcome to OB, tell us what you drive and what you have done to it in the way of modifications or what you plan to do.