Some Loser,
92 Atk Choice Band Ferrothorn (+Atk) Gyro Ball vs 0 HP/0 Def Latios: 112.9% - 133.55%
Guaranteed OHKO
***Brave 0 Spe IV Ferro vs. Timid 252 Spe. Latios***
92 Atk Choice Band Ferrothorn (+Atk) Power Whip vs 252 HP/252 Def Politoed (+Def) : 103.55% - 121.83%
Guaranteed OHKO
Problem, Toed?
92 Atk Choice Band Ferrothorn (+Atk) Power Whip vs 4 HP/0 Def Ludicolo: 100% - 117.95%
Guaranteed OHKO
92 Atk Choice Band Ferrothorn (+Atk) Power Whip vs 4 HP/0 Def Kingdra: 81.46% - 96.03%
2 hits to KO
92 Atk Choice Band Ferrothorn (+Atk) Power Whip vs 252 HP/40 Def Tyranitar: 100% - 118.84%
Guaranteed OHKO
And my personal favorite:
92 Atk Choice Band Ferrothorn (+Atk) Gyro Ball vs 0 HP/0 Def Thunderbro-T: 62.99% - 74.03%
2 hits to KO
***Same Ferro vs. Neutral 252 Spe. Scarf Thunderbro-T***
EDIT: For a CB set, you really only need four attack moves (Power Whip / Gyro Ball / Shadow Claw), and then feign the Band via a Status move (I had Leech Seed, though Stealth Rock is handy for when I play in OU every so often). For the Fourth move, Explosion also works.