Does anyone know if the factory ammunition pushing an 115gr OTM round will meet or even come close to the original velocities specified for the 6.8 round?

If not, how much slower will the factory ammunition be?  

Does anyone know how these potential lower velocities will affect terminal ballistics?

2500-2600 fps from 16".  Maybe a tad more but I doubt it.  Terminal performance won't be quite as good  as what was originally predicted, but it will still be measurably better than 5.56.  

If you are asking about hunting applications, I would suspect that softpoints, either conventioanlly constructed or controlled expansion designs, would be the preferred bullet to use, and in that application 2600 fps will work just fine on medium sized game out to 250-300 yds.  If you go with a longer barrel, velocity will be better of course, but if I'm not mistaken, the 2800 fps quoted by remington was with a 24" barrel.  So you can extrapolate out the probable velocities for 18", 20" and 22" barrels.