Hmm, I have a 950, and I find it slow for complex image PDFs. Some of my image based PDFs bring it to its knees, but perhaps I could use Adobe Reader Pro to covert the PDF to a "mobile" version, which might help. I've seen this on at least two image PDFs (which are Greek on one page, and English on the other). Also, in my very simple annotation tests, I found the annotation to be slow, although I've not used it much, and I'm not sure on which texts (epub, PDF text, etc). Also, I've not done tests with annotation searches.
In summary I find the 950 to be fine simple PDFs and epubs, but anything else just seems to be at least somewhat taxing and slow. Look, even large text based PDFs (like a massive Cambridge history) bring it to its knees (although I could convert the PDF perhaps to a "mobile" format). Maybe others could chime in with some input. I don't consider the Kindle to be better for PDFs, but maybe the Pocketbook 902/3 or Onyx M90 merit your attention, but they're MUCH more expensive.
EDIT: look like the M90 is NOT what you need either, it's too buggy and slow:
https://www.mobileread.com/forums/sho...40#post1716840