I won't go as far to say you can get a 750+, but I think you can get a really great GMAT score even if your weak in those subject areas. In my experience, a lot of people over study these subject areas--the truth is that probability/combinations/permutations aren't frequently tested on the GMAT. If you're doing well in the section you'll get just a handful.

A better strategy is to make sure that you are fundamentally grounded with algebra, arithmetic, number theory, and geometry. You're guaranteed to see a lot of those problems!