If GRRM only had 1 book to finish before GoT caught up, we would still be on schedule.

But GRRM has to finish 2 books at the minimum, so there's almost no way A Song of Ice and Fire will be finished before Game of Thrones surpasses it. GRRM has to finish book 6 this year, and finish book 7 within 2 years so the show can plan off of it.

I hope the ending of the 2 are not completely different. TV shows want their happy endings, but GoT should be a bit darker than the usual stuff.