Hidden hand isn't possible on the Arminius. You want counterbalance and braced frame for max stability. Already has huge aim assist but there is one scope that provides some as well. The other perk slot doesn't have anything game changing available to it so I wouldn't hold out if everything else is there but if say, ideally, u want something like crowd control, army of one, maybe danger close. You can search any weapon out in the planet destiny database or the armoury to see every perk available in each slot for any weapon or armour piece.

If hidden hand isnt available, the next best would be hot swap or army of one. Not a fan of crowd control on a low impact gun. 15% dmg increase would be hardly an impact.