When you test stuff with multiattack on it (DA, TA, QA) make sure to compare the results with AM3 on and with AM3 off.
With AM3 down you get full return from multiattack.
With AM3 up you get half of it (it will apply only to the OH hits, not to the MH)
Sometimes this will create a difference between which item is better for a specific slot.
Also if you're testing stuff that has "attack+" on it, make sure to test it with attack uncapped (so that that att+ on it matters) and after that test it with att capped, to see if the piece still wins even when att is capped, or if something else wins.
Altough truth be said we should be talking about "overcapped", because PDL allows you to gain benefit from attack, to a certain extent, even after your att is capped.
Situations on content that matters where BRD is completely overcapped aren't that common I would say.
On some 6men content where you zerg with lotsa buffs maybe, but everywhere else more often than not you're not gonna be att capped, no way you'll be overcapped either.
My rule of thumb when evaluating small differences: focus on the global picture.
Let's define 4 different situations, and let's say we're comparing piece A, B and C for the ammo slot, ok?
Situation1: A wins by far
Situation2: A wins
Situation3: B wins, barely ahead of A
Situation4: C wins
Now you have to consider a few things. More often than not the frequency distribution of these situations will not be even. It's subjective to the way you play BRD, the content you do etc.
If you play mostly Situation 1, 2, 3 and rarely play 4 the answer is easy: just use piece A and simplify things.
But what you never play situation2 and 3, rarely situation1 and everyday situation4? You might consider using Piece C
These are things you have to consider. Sometimes some pieces are so rarely used it's not really worth the inventory+1. But again, it depends on your inventory strain etc.
Also never forget accuracy. It might be irrelevant in some content, but very important in other events.
Last but not least: do not ignore the defensive capabilities of some items. Sometimes the damage difference is so insignificant and one piece offers say something like 10DT/50Meva over another piece, that in such a situation I would probably suggest the piece with slightly less DPS but 10DT and +50Meva