In regards to GS Cap 1, here is where you have to be a little careful with GPA. The GPA point you reference is based on one sale last year. GPA only has five sales of a gem mint copy of that book since 2010, or one copy every 2 years or so. The book has traded higher in private transactions and there are only 7 copies of a popular title in the popular run headlined by GS X-Men 1.
It is always a bit counter intuitive, but I have usually made more money buying books where I set the new GPA record high price than buying books at a GPA discount.
if you can find a GS Cap 9.8 for $600 bucks, I would hit it fast, but I suspect that those days are gone.
Anyway, that is my 2 cents.