Cobra can work, honestly his own slot 5 would be a great (cheap) alternative until then as well.

Any solid stat stick can work in the interim. Siege, Power Cell, even a Skrull Energy Rifle.

We have a good autocrit and a good autobrut, so flat damage goes far. Brutstrike to give us higher conversion of Energy Overload to a brut is also high value, so if all options available I'd probably go for Siege.