1) Those numbers are indeed accurate, and are in the guide.
2) There are calculators that allow you to manipulate your stats and see how your damage would change (http://valk.dancing-mad.com)
3) They both have equal STR values, so I would mix and match depending on what you need in terms of accuracy, and which piece is the most valuable using the previously discussed stat weights. If you're aiming for defense stats, which shouldn't factor in too much but that is your choice, I'd aim for an even mix of physical and magical.