Attic insulation over IBA

[Eric H]

I recently added 2 Razor to an existing wash. The contrator did a terrific job except there is no insulation above the IBA's. I do have windstar doors but I would like to add the insulation to the attic. I met with an insulation contractor who wants to insulate to R-60 which is about 30" of blown cellulose.
Is R-60 overkill?
Is cellulose a bad choice for this application?