And there (image PDF) is your problem. Even for mobi and azw3 books every page that has an image triggers a full screen refresh.
Since you Kindle is already jailbroken you can use
KOreader for reading PDFs. The original (text based) PDF, not the output (image pdf) of k2pdfopt.
I've just double-checked (I've used fiction type book , non-image PDF) if KOreader is doing full refresh after every page and it's not doing that, there is full screen refresh every 6 pages.
KOreader does pretty good job with re-flowing PDFs.