@ Mrs.O.
A game I can play along with at home!
I played your 2nd video and turned pages in synch with you. My 4.24 speed seemed much more like your 4.9 speed than your 4.24 speed.
I used a ClaraHD with OpenDyslexic and NiLuJe's latest MiniClock version and tried 2 different books, a short one with short-ish chapters and a long one with longer chapters. The results were the same.
I'll confess to all my books having been edited to death to remove excess HTML/CSS cruft before they ever reach a Kobo device. Also page turning speed has never been a big concern of mine - fast enough's good enough.