My math went up a bit, and my verbal went down a fair amount. I took a lot of math courses in college, and the verbal section, I should have studied for it by memorizing obscure word definitions, like everyone else seems to.
I don't know if there's really a good way to estimate a GRE score based upon an SAT score alone. If you're concerned about it, you might want to check out some practice tests. No clue where you might get one of those, but I know they exist.