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To be honest, neither of these may be ideal for you. It is always best to have the book specifically written for the software release you're using. The Photoshop CS6 and Lightroom 4 book will obviously be helpful for LR4, but depending on the differences between CS5.5 and CS6, portions of the Photoshop sections of the book may not be helpful.
Here is a link to a page on ProDesignTools.com (who is affiliated with Adobe), which offers a A New Feature Version Comparison between CS5.5 and CS6: http://prodesigntools.com/compare-ver.... This may help you determine whether the Photoshop sections of the CS6 and Lightroom 4 book could be workable for you.
O'Reilly Media Customer Service Team