We’ll see a full-strength Arsenal side out there most likely: Wenger will not want to throw away this chance of getting some silverware after a 5/6 year absence.
But then again they are still battling on all fronts and in a good position in the PL, so he might give a couple of his “reserves” a run out to keep everybody fresh.
Either way I’m going for an Arsenal win, never been a huge fan of Birmingham and the gunners play good football (although they have been dirty beggars recently!)