I'm in the same situation... though I'll presume its abilities do follow the same laws as ours.
easiest way to test it would be to unequip all of your gear. record your pets average firebolts across a sample size of say 10, then equip all your gear. record how much +damage the pet gains from it, work out how much of a damage bonus the firebolt should get using the coefficient of 57.14% and then record another 10 firebolts. if the average is very similar to the 'gear unequiped-firebolt' data+ predicted damage bonus then you'll have your answer :)