Speed depends on resolution. Comic books I do at 150 dpi, color (unless I really like the art, then I set the resolution to 240 or 300). At 150dpi, the scanning portion of the device moves faster (or if sheet feeding, it zips it through faster). The higher the resolution you program, the slower the scan, but not terribly slow. Maybe... 8-10 seconds for a full two pages? If the book is old and yellowish, I'll go with a higher resolution, too.
The higher the resolution, the more accurate the OCR -- or the better looking the PDFs if you go that way. Paperport has a built-in PDF-making ability, but I suspect other similar programs do, too.
Also, if you can sacrifice/dismantle the book, that should speed up scanning because you don't have to press the book down to try to get it as flat as possible. If the binding is loose or limber, this may not be a big problem. If it's a library book, well... But if you can find books at used book stores (our library has one, for example) or garage sales or thrift shops, dismantle 'em, I say
