To be honest 6” is a large amount of girth for you to gain. Gaining 1” is a large gain and not everyone can do it, but that doesn’t make it impossible. I think 5.5” is definitely possible if you dedicate yourself greatly to the process.
The big gainers on here, in my opinion, are the ones who pay close attention to their penis and tune their routines perfectly to what their body reacts best to. Pay attention to what works and what doesn’t, pay attention to how often and how long of a routine works for you and what doesn’t. You have to experiment a bit, but once you find the sweet spot for your penis, gains will come.
That being said, do the newbie routine first. But don’t be afraid to tweak it to experiment with what works best for you once you’ve got a bit of experience. And by this I mean changing the amount of time spent per exercise and the amount of reps and amount of sets. Don’t add advanced exercises as part of the experimentation. And it goes without saying, don’t go overboard, 20 sets of 50 jelqs isn’t going to do anything for you but hurt you, the same with hours on end of stretching.