I took the Mcgraw hill tests from the CD of an older version of their book (2007 or 2008 I think). I found those questions a notch easier than the real GMAT. I stopped using Mcgraw Hill book and the tests after I tried the Manhattan GMAT
stuff which was probably a little harder than the real GMAT test (I have taken GMAT twice so I knew the level of questions I'd expect to see when I first used the Mcgraw hill stuff). I'd say most of the questions on it are 600-680 level questions.
I can't remember my score from the Mcgraw hill CATs - but I remember thinking that any score that comes out of these questions is not going to be accurate.