it depends on the mob really. As mobs get higher def, the forcy starts to outdamage the osm, even on crits. I just generated a table for you using LastHour's Damage Calculator. Not exactly your stats but i just guessed :P
Dual Osm 40cd in Bm2
http://img145.imageshack.us/img145/5407/osmo.png
Dual Forcy 17cd in Bm2
http://img834.imageshack.us/img834/38/forcy.png
All of these damages are done per hit, not for the duration of the bm2. So imagine the extra damage when u factor in how many times u hit in over a minute in bm2 with second series retarget (kick retarget)
Forcy s amp is even better in Bm2 than forcy DB. Bm2 was done on derk. Forcy 17cd isnt too much more expensive than osm 40cd, considering you need a seh for the osm. Also, all weapons were done at the same + (+11).