The producers confirmed yesterday (on the Deadline site) that they are shooting for 8 seasons - 80 episodes - for GoT. They have also said several times that they cannot delay the show for two years, put the show on hold or use the D&E stories as filler movies or something. The show has to keep moving: delaying by a year or even just a few months might risk losing some of the actors to other projects.

GRRM appears to be unhappy with this. He has said that he thinks they can in fact delay the show or skip a year (as THE WIRE and THE SOPRANOS used to), but HBO have said they hated that old model, the viewers hated it and they now only want to have annual seasons, so that's not going to fly. Because of this, I think it is likely that HBO will overtake GRRM, but not until after TWoW is released.

Structurally, Season 4 will be the rest of ASoS with some AFFC material brought forwards (the Croatian city of Split is rumoured to be standing in for Braavos) and even some ADWD material included (Bran's ADWD storyline is likely to completely unfold in Season 4; there's nothing else for him to do). There'll also be some new material: it sounds like Osha, Rickon, Ramsay and Theon will still be on the show when they don't appear in the book at all. It also sounds like they are sidestepping around the Kingsmoot by having Yara be on the other side of Westerso when that takes place, meaning they don't have to cast Euron or Victarion until Season 5. That leaves Season 5 to handle the bulk of AFFC/ADWD.

Based on the producers' comments, it sounds like their plan going forward is to concentrate on the show's major existing characters (Arya, Jon, Tyrion, Daenerys, Sansa, Stannis, Davos, Cersei, Jaime etc) and new characters will be included only when absolutely necessary. So, compared to the 20-odd new characters that Season 3 introduced, Season 4 will only have a few (only Oberyn Martell has been cast, and they are also looking at casting Mace Tyrell and Ellaria Sand).

This makes me think that Season 5 will be a 'streamlined' AFFC/ADWD. The ironborn and Dornish storylines will likely remain, but be fairly brief compared to their dominance in the books. I can also see Oldtown's importance being reduced, and maybe Volantis's. The focus will squarely be on the existing major characters. This is likely the source of GRRM's reported unhappiness with some aspects of the plans going forwrds, as he doesn't want them to lose some of those characters and storylines. I think their goal will be to hit the battles at Winterfell and Meereen at the end of Season 5 (which means they'll be filming TWoW material NEXT YEAR) or the start of Season 6.

This will give them 3 seasons (Seasons 6-8 ) to cover the two books of TWoW and ADoS, which GRRM has already said will be as long as ASoS and presumably as packed with major plot events as the series winds up. One-and-a-half each should get the job done.

On that basis, I think it's probable that the show will overtake GRRM somewhere around 2017, by which time he should have TWoW out.

As for the books, GRRM is 25% done with TWoW (in terms of final material; he has a lot more in drafts) but has made slow progress due to the other projects he took on post-ADWD in a burst of optimism. Almost all of those other projects are now gone and he recently told Conan O'Brien he is now making rapid progress on TWoW. How rapid, and if it's enough, remains to be seen.