I've had a similar problem with PDFs in both Acrobat and Preview for some time, but found an effective (if bizarre and slightly annoying) workaround.
I've found that if I open the trouble PDF in Preview, then select File > Print > Save as PDF, overwrite the original file, then close/reopen the PDF, suddenly the PDF is liquid quick when scrolling. It's strange. This seems to have something to do with how Acrobat generates the PDF versus Preview.
The annoying part is that I find myself manually repeating this process for a lot of PDF files that I deal with for work. I would *love* to discover a macro or Automator script that would let me batch "print as PDF" a bunch of slow-scrolling PDFs. If anyone has any ideas, I would be eternally grateful...