It's very unlikely you'll be able to compare opening books just by playing against them. Main lines will be approximately same in all books, what you really want to see is how "wide" these books are, do they contain only a few main lines, or plenty of variations as well.
The easiest way to do that would be to convert the books back to the readable (PGN?) format and see how many different games are included for a particular opening.
Might be easier to do that using some software than comparing by hand. Even better if the software can read the books directly, this way you don't lose any information while converting books to .PGN format, but you'll have to be able to program for that to happen, because I don't know any ready-to-use software for the books comparison.