1st: Yes, the driving bands will increase drag, all other things being equal.
2nd: Modern aerodynamic theory could probably be used to determine the additional drag to a acceptable degree of accuracy, however that would only work for the bullets as they sit in the box, and would not apply once they have been fired. As wapiti13 mentioned, the deformation left by the lands and grooves affect the ballistics, and do so even more when driving bands are present. The exact manner of the change the barrel has on the bullet should vary from barrel to barrel, as both land and groove diameter are not set in stone, and virtually every different rifling option could have some effect (twist rate, #grooves, shape of grooves, etc.)
What I have been trying to imply with all this is that I feel in this case the only way to know EXACTLY how the driving bands affect the B.C. for you is to carefully experiment with them in your barrel. However, most of the effects of different barrels would be minor, so if someone did go through systematic testing of banded vs. smooth I would expect the results would be reasonably close to your own.
Just a theory, feel free to contradict.
Carl