I just recently read books 3 and 4. Parts of them at least.
3 should be divided into two seasons. Season 3 ending with the you-know-what scene in episode 9. Season 4 ending will be the ending(s) of Storm of Swords (which would be epic to watch.)
Book 4 is not really adaptable to the TV show. I guess they will alter the story by book 4 so no point in making any assumptions.