Doghouse,
I think that there is a threshold or a level to which Topamax "peaks" for each person. I have a best friend who has migraines that are VERY similar to mine, My Topamax dosage was 400mg daily (which is twice the recommended dosage)...hers was 75mg, it varies with each person.
Stick it out, when I could afford Topamax (no insurance right now) I felt better than I ever have, it is at least worth a try.