I use Goodreads to track too - I don't think I'm a very good example as I don't have the best long-term memory anyway (eg don't remember lots from my childhood). I think I put stuff into 'don't need to keep that info' piles and let the memory fade away. So if you have a long-running crime series, it's quite common for me to forget which ones I've read. Individual books I'm more likely to remember well.
When I'm reading a trilogy etc and I start book 2 years after book 1, the details usually come back to me fine. But if I'm watching a movie version of something I've read, I won't catch little mistakes (big ones yes), in the way that my kids can.
I remember the book in detail in the moment, as I need to - but can't rely on knowing it forever. But I think how fast or slow I read hasn't got anything to do with it, it's just my dody memory.
For the record, I think I'm an average 'fast' reader. I read about 70-80 books a year but can read a book in a few hours or go a few weeks without reading any. Literary books can take me ages to finish, but a thrilling page-turner compels me to read as quickly as possible.
I do have loads of unread books - mostly on kindle as I tend to be more particular about things that actually take up space now. I never used to be and when I worked in bookshops I would buy hundreds. But I realised that even at a good speed it's going to take decades to read everything that's already on my want-to-read list!