[Lord Commander Erus]

That seems fairly balanced.. I might even make it an even 15/15, for 30 over all. Though I would make it (to give it even more balance) that he can use either or, but not both.

Basically, at the start of the assault phase (of either players turn) the player must declare which weapon the Captain is using. The +2 str spear is two handed, and therefore for using it as the primary, you get no +1 attack bonus, but you do get the +2 str and power weapon effects (useful against light armor like a dread, or high toughness foes!).

If he decides to use the sword, you get +1 attack for having the spear still, and just the power weapon effect on the sword.

That to me sounds fairly decently balanced, and does realistically reflect the way the weapons would operate in real combat.