I have just received CPP Books 4 & 5 but haven't started on them yet. I'm on Book 3 of the series after completing Alfred 1-3 in July. My main book at the moment is Masterworks Classics Level 3. I chose CPP as my supplementary series as I wanted a complete contrast to prissy little sonatinas and minuets. In that respect, it works.
Looking through Book 5, I would say that the end level is well below that of Alfred 3. I don't know what that would be in exam grade terms, if that's what you want, but probably in the Level 2 area. Pedalling, for example, though present in Book 4, seems to have been dumped completely by Book 5!
My overall impression of CPP so far is that the pieces, though often the same in both books, have better arrangements in Alfred. Also, the Alfred pieces are mostly on YouTube and that can be very useful.
Perhaps someone on the Teachers' Forum could give you a better idea of the exact level of Book 5? I think you'll find that not many people stay with CPP to the end!