The two factors that determine scanning speed are colour depth and resolution.
For simple black and white pages then a 2 bit (black and white) scan would be fine, possibly 8 bit greyscale if you need to improve readability.
Scanning at a resolution of 200 dpi should be plenty.
Try to compare the scan speeds of scanners using the same settings (colour depth, resolution, page size). Also, in your case, I would recommend a scanner with an ADF (Automatic Document Feeder), this makes it MUCH easier as you just load the stack of pages and push the button. if the pages are double-sided then you will need an ADF that duplexes.