I don't care how long a book is, most are too short anyway
Besides, people here mention the Outlander series. I have them in my library upstairs. But one Outlander book is as large (and thick) as the entire collection of my Princes of Amber from Roger Zelazny. But the Outlander book has normal pages and normal letter size, the Princes of Amber book has very thin paper (I always am reminded to that paper you make cigarettes from...) and a very small letter...
So, it's relative even in pbooks!