Let's not blow this out of proportions. It's an improvement for a single game (a 3 year old game at that). While AMD provides precise improvement % for all windows titles, they only say "significant" when it comes to L4D2. This can mean anything between 20% across the board (very unlikely) to maybe 10% when running crossfired 7970s with AA and AF enabled. Besides one line from AMD, we don't really have much to talk about.