For my process of learning, that's probably the most important aspect. The closer I am to the sound the more fun I have and more likely to feel that I should play it live. If I don't find it, or it's not close enough I tend to shy away and definitely won't play it until I find it.
In my experience, the sounds are different from song to song - at least on the studio recorded version. I am finding a lot of stuff live, it's generally a generic sound.
I also find it difficult to start from scratch when discovering the song's sound. At least that's my problem. Also, the settings I find online is generally over-driven too much. Granted, you talked about FFDP and Metallica, some very distorted sounds - but they do have limits.
How authentic can I get? Pretty damn authentic. But, other people have told me that. It also takes me a long time to perfect the sound. Yeah, the sound is 90% of the process right there. At least that's my motto.