Well Mantle is out, kinda. DICE has enabled it on their patch and will continue to update their renderer with AMD updating their drivers and the Mantle API along the way.
Basically, you are expecting 10%-40% increase in performance depending on system configurations. Expect to see huge performance boost with high end 7000/R9 series card coupled with midrange CPUs/APUs. Once you reach the high range CPUs/APUs you get around 10% boost.
AMD's Master Plan:
1. Lock in their dominance console hardware market essentially ensuring their presence in the next gen console come 3-5 years.
2. Defeating NVIDIA's performance gains (brute force speed) by software optimisation rendering current NVIDIA's wins moot and turning the game devs to start exclusively build games on AMD's API (linked with point 1).
3. Fortify the low end and mid end CPU market share by draining consumers from the high end segments with longer longevity and better CPU performance. In other words steal gamers from Intel's highly prized high end CPU market to buy their cheaper mid range CPUs allowing them to spend more then on AMD high end graphic card market (Intel gets a double not only in losing i7 users but also their APUs). This also targets the laptop segment.
Well those are my impressions, AMD MAntle is out there to give you a boost in performance with the current gen of AMD products and not with promises of next gen ones. While at the same time crippling Intel's high CPU dominance and any dreams of challenging AMD on APU front and locking NVIDIA out of the graphic card market completely. And this is on the PC front we are not even talking about the console markets and possibly the ARM market (since they are testing the waters with their new ARM servers).
If this takes off just like the 64bit revolution they started all the way back with the Athlons CPUs you will see Intel making compatible GCN APUs sometime in the future.