90 percent that it will not be very bright and 99.99% that it will NOT be a historic record.
Why? For several comets from the past decades I remember, the expectations how bright they will be, were very high. With a naked eye we then hardly saw one or two. This is one reason.
The other one is that the composition data of this comet and of all the others should be very good, for such claims. What is not a case.
Try to predict something important in a way, that it will be easy to judge it in 2014, how (in)accurate your predictions really were. Don't leave too much space for a doubt what was really said.