basicaly its like this.
if you give your pet gear, be it weapons or armor, the pet will decide what is best and use that.
so if you give a 29th pet cloth armor it should not use this as it is not as good as its natural armor, yet if you give it Plate armor that is better then its natural armor (some of the mage summoned stuff) it should equipe that gear.
as for weapons. ive seen heard so many different things its not even funny.
on lower level pets i have seen weapons make a HUGE differance in their ability to hit harder, not more often, but harder. it seems the attack speed of pets is set unless hasted via item or spell. the higher level mage summoned weapons do hit much harder then 4th-12th level pets do without weapons.
with the higher end belt and muzzle the pets at lower levels are almost unstoppable. the haste seems to fully effect them, note i said seems, and i know the AC+, STR+, HP+ does affect them 100%.
i have a 12th mage im playing with just as a toy. took some old junk gear i had laying around and gave it to the new mage toy.
if i take some coin and hit PoK and donnate to a 63+ mage to summon full pet gear (i normaly get 2 sets or muzzle, belt, and only 2 swords as my pets can not DW yet) and i get mana preserving item, spell haste, and DD my little mage can solo things that are way out of his league under normal situations.
at 8th i took my mage to the mids in nek forest. with the white cloaked goodies love to hang out. one of them at 8th is deep red. my pet almost soloed him. i had to heal him 1 time with my cleric and i nuked the guy 3 times before he fell.
at 12th the guy can still be yellow, but more often is only even con. my 12th pet owns him with that gear and i only cast 1 time just to get 100% of the xp for the kill.
hope that helps a bit.