This might come a bit late as I’m not sure when your flight is, and if this is the case, my apologies. Having said that, it really depends on what you would like to focus on. Since you mentioned
my suggestion would be to concentrate on IPv6. Review the original RFC and some of the more recent amendments.
Now if you’re looking for something very specific, an RFC will get you what you want to know. But if you’re looking to understand a concept or a protocol better, reading an RFC would probably not be the best way to do it. There’s just so much info about any one specific protocol or topic, that you can’t get a good overview and understanding of how it works.
You may get 20 pages with intrinsic detail about a specific field in a header that is used occasionally, but that’s too much like a fly on a painting if you get my meaning. You need the big picture description to gain an understanding. RFCs should more often be used for research of very specific functionalities when you need them.
Now where should you go to do such reading? Well, I don’t have a silver bullet solution for you, however, some of Cisco’s books are quite useful as are Rene’s books. But the Internet in general is such a good resource when you know where to go and how to search. It just takes experience I guess to know how to identify good sources of info and filter out the rest.
I hope this has been helpful!