With Keen: 17-20 x2 (120%) With IC: 15-20 x2 (130%)
With OC: 14-20 x2 (135%) With DC: 14-20 x3 (170%)
So ignoring confirmation rolls and damage resistances it's a 40% loss on crittable mobs. With the current state of the mod - the trash should be instakilled, not beaten down - I'm still not convinced to keep OC/DC.
If you get +2 Dex for checks, or +2 Cha for more dmg vs noncrittables, then that's an attractive tradeoff. Otherwise ("imo") it doesn't seem really worth the trouble, because regardless of crit/trash/targeting argument, your primary function as a tank should be to help the cores complete spawns faster, and unless you're a total carpet in the first place, for that purpose 60 more hp + some defensive statistic doesn't outweigh losing Str tank advantage of OC/DC (debatable usefulness depending party/run in hells for clearing spawns more efficiently, but no one can really deny it makes you a better killing machine basically anywhere else). But I think +2 Cha->1 or possibly 2 (cc pal 50% bonus) more pts of phys is justifiable.
+2 Dex or Cha would be prolly most tempting option for me. I think +2 con is a wash (admittedly synergizes w/ toughness tho). +2 Int is nice, but I don't think as nice as OC/DC (+63 more skillpts would basically net +1 AB/AC from CA/CW?).