I have no idea. If you go to the 'is St Andrews underrated' thread, you'll see that the whole Uni has become incredibly fashionable to lots of people (especially Americans, 15% of the University now), and as such, is able to command stupidly high grades for certain subjects. It's a very good Uni, but its results in research, teaching and employment prospects don't make it any better than a lot of other Unis, but it seems to have marketed itself incredibly well in the last decade. Durham's history dept seems to be in the same boat.
From what I know of the IR course, its pretty good. It's not world or even UK leading, but if you get a first from there, you'll still be doing well. Quite why it (and the wider University) is so, so overwhelmed with applicants now, is really quite puzzling. Third behind Oxbridge now for those from the highest earning backgrounds, yet its results (IR included) are nothing out of the ordinary when compared to a lot of other Ancient/Russell/1994 group Unis. I guess whoever put the St Andrews brand out there in the last decade, deserves enormous credit. However, back to the point- I reckon if you don't get in there, and many AAA-AAB applicants wont, then I wouldn't be too disheartened, the grades (again, like Durham's history dept) are a artificially high right now, and there are plenty of depts out there that are on a par with it.