Back to savoring a slow read (not that the previous discussion wasn't interesting): I read at the speed I read (and sometimes at the speed the author
allows me to read at--if that should happen to be slower than MY speed).
Long story short: I don't take any pleasure in purposely reading a book at a pace slower than I could comfortably be reading it at. So the only way I could "savor" a book would be to read it in shorter sessions with more time between those sessions. I couldn't imagine anything more frustrating than forcing myself to go through longer periods of NOT reading a book that really want to be reading.
But then again, I've never really been bitten by the "I never want this book to end" bug. I
love endings—great ones, especially. The more the merrier I say!
BTW: I loved the book the OP is referring to here--DeWitt's
The Sisters Brothers (shortlisted for the Man Booker and the Giller Prizes, among others). Read it in about 3 days.