Gonna have to be honest. I'd take Archaon. His 10 Str5 armour ignoring attacks will put any Ironbreaker in his place.
Take plenty of hounds, you need that Screening.
If Archy is a no no, a Khorne Lord on a Jugger with Ranged protection and a Sword that ignores Armour is a must.
Marauder horsemen may also have a place in your army, with flails, you can use them to silence those guns!
Thats all from me, but I stress Archaon. If this match is important, whip out all the cheese you can. There is no rule against it.