Hm... if rage and mourning produce an unstoppable combat-state, the ability to weaponize spousal death would seem to be useful. But first, we must confirm conditions
the first step would seem to be to create a party fort to encourage large numbers of lovers and marriages, while defending the fort with cage traps. Danger-room everyone to equal skills, while stockpiling captured goblins You won't be able to perfectly equalize stats, but a large sample size will help. The ranged goblins and non-goblin captures would foul the experiment, so use them for training or just pit them to recover the cage.
Build two rooms, a "sample" room and a "control" room. each one is 11x11, bisected into two 5x11 spaces: the control room uses walls with a lever-linked door, while the sample room uses vertical bars, one set linked to a lever in the same place as the door.
Station one member of a spouse pair on one side, the other in the opposite half of the room. Let goblins into one half of the room, to fight a single member of the pair without interference from the other, until the first member of the couple is slain, then open the door or bars that separate the two halves, and permit the spouse to fight the killer and a similar stream of goblins until also slain.
Compare the kills of the first spouse to the kills of the second in number and quality, and compare the systematic difference (if any) between spouses that were able to see their partner killed and those that were not allowed to witness the event. It may also be prudent to test the same setup with dwarves who do not know each other, to see if it is simply military witnessing death that causes outstanding feats, if in fact outstanding feats happen.
One thing is certain... using danger rooms to equalize skill differences means we will need a LOT of melee goblins
Edit: It's supposed to be a throne, I'm pretty sure. Magma for the magma throne.