I am getting ready to purchase a new Ultrabook. Is a 12.5'' or 13.3'' screen size large enough to effectively use BIAB 2014 & Real Band?
While it would probably run BB, I would recommend that since you are purchasing new, that you seriously consider paying a little bit more for a model with a larger screensize.
If for no other reason than my favorite at purchase time, I try to let the idea of "future proof" guide part of the decision.
Never know what new thing is coming down the pike, but in this instance I think its safe to say that the trend has been moving to larger and larger screensize and having that available when needed can solve problems even before they arise.
What I can tell you via empirical observation is that, during the beta testing and afterwards now, I've broken out an older laptop with 14" screen to check out the new BB on, and while it is usable, I've got to say that the more modern widescreen laptop I've got here is MUCH easier to view, easier to see the Chord Sheet or Lead Sheets when playing and practicing, so I wouldn't think that the choice you are looking at here would be the best situation for such.
Have Fun,
--Mac