I have found a solution. It took time, maybe a lot more time than it would've taken some of you, but I'm persistent.
First, I synced the notes in my 950 with my computer Reader Library software. This took awhile. I knew nothing about it, so first I read up on it based on Bookworm Girl's post. Then I couldn't find the Sync button! Who knew it was in the 950's menu? I wasn't sure if I hadn't done something right. I was looking at all the buttons on the bottom and top of the library screen, then at the very top of the screen menu buttons, then when I found out that I can sync by folder, I was looking for a little sync icon next to each folder when I hovered over it. It was just so unassuming, sitting there like a bad little boy taunting me, looking like just another 950 folder that I was ignoring.
Once I found the sync button, it took forever to sync. I had to stop it multiple times thinking it would never end. For instance, the longest I left it was over 30 minutes and it never finished (I do have a lot of notes though). So I thought I was done for. But then I checked and voila! It had transferred all the notes over. At least, I hope it's all the notes. From the random parts I checked it seems to be all of them. Although, it didn't transfer all the books which I thought it would, just the notes. But maybe that's because I never let it finish.
Anyway....that's all besides the solution. But it is nice to have it synced now as a backup.
As mentioned in earlier posts, I was considering breaking the book up into separate sections. I have no idea how to do that, and no one posted any info on it, so I gave up on that. It just seems way too complicated. But after syncing, another idea came to me. If I could have multiple copies of a book, I could trade them out as the notes slow down and start afresh with another copy.
I figured though that if I just made the exact same copy it wouldn't work. They'd just go in together and for instance if I synced, it would sync with both books and make a big mess. So I figured I must somehow change each copy. Have I mentioned yet I'm not a techie? LOL. So it was like trying to see in the dark. It was a LOT of hit and miss.
I finally hit upon changing the file title and book name. Didn't work. I'd add the new file to the library and it'd add the same exact book. So I tried putting it into calibre (from googling). I've never used calibre but I had downloaded it when I first got an e-reader at the advice on mobilereaders, then just left it there never using it. So from google I heard I could change the title in calibre. I could, I eventually found out....but when I added it to the library it still wouldn't change! :O I could rename it "Billy Bob's Holiday in Yonkerville" and it'd still show up as its actual title in the library. *sigh*
I've never converted a file type in calibre, but I thought eh, let's give it a try. I didn't even change the file type...I converted it from epub to epub (it was non-DRM public domain so I don't know if this would work with DRM books). Then I put in in the library again for the thousandth time...and finally, it worked! It showed up as a different book with a different title and file name, but all the same contents inside! FINALLY!
Now that I know what to do, it should be easy. And I transferred it to my 950 and tried it out, and it's perfect. No more 15 second slowdown on the "new" book. This may not sound like it was too hard, but to me it was like performing brain surgery to figure out.
Of course, I would advise to only do this on books that it is legal to do so with. I'm assuming it must be legal with public domain books as I was doing, but I can't advise on any other type of book.
Bookworm_Girl, your advice was invaluable in getting me started. I am also going to try to back up my notes another way as you mention, but I need a rest first before jumping into that bog. Also, I am going to get an SD card and put it in to hopefully help speed even more.