I had genuinely forgotten most of GC and was able to use Chad's videos to get myself back up to speed. Although I won't attribute my success to the actual class I took to any large extent, I'm sure that it made it easier for me to re-learn everything the second time around.
Organic Chemistry was a different story, though. I had just taken the class and remembered a pretty good deal from it. However, Chad helped me brush up on all the things that had slipped away over the course of the summer.
I wouldn't expect a 30 with Chad alone, especially if you haven't been in school for years. I do, however, think that knowing all of his videos inside and out can practically guarantee you a 22. I agree it would be wise to use KBB to brush up on any topics you weren't very confident about. However, I didn't use the KBB myself for the sciences; I relied primarily on Chad. I did the Destroyer as well, but didn't find it to be nearly as effective.
If you REALLY know Cliff's and Barron's AP bio books, I once again think you are guaranteed at least a 22. My sneaking suspicion is that people who don't score so well after using these books *say* they learned them, but they didn't really.
People have a habit of spreading themselves too thinly amongst a ton of different resources. I say pick a few resources, REALLY learn them, and you're good to go. It's what I did. I never even took a practice test. However, I am admittedly very good at preparing for tests. I can figure out what to focus on and what to regard as "fluff." You seem like a smart guy yourself, so I bet you have similar skills.
If you have any more questions about what I used and/or how I studied, you're more than welcome to shoot me a PM! 😀 My breakdown is also in my signature, and I talk about a lot of these things in it.