This is not a game btw Andy, its a benchmark designed to highlight the differences in performance between Mantle and DX.
This. Just for the record, I had back in February ~ 36fps vs. ~59 fps, while today I have ~ 36fps vs. ~50 fps. Don't know what they've done to it, but at least for me it looks like the DX performance is about the same, while Mantle performance went down about 50%, from an improvement of ~ 63% to about ~ 42%.
It' clear that if you build your game going for Mantle full support and features with insane number of batches (justified, of course), DX cannot catch up. That's the whole point of the benchmark.
Also notice when you talk about increases:
X card could do theoretically 107FPS
Y card could do theoretically 120FPS
X card could do 100fps + Mantle 105fps
Y card could do 90fps + new driivers 110fps.
What that tells you? Well, 1st - the previous driver might not have used that Y card to the best of what could have been done without the latest research that enabled even more performance under DX; in contrast, X card would have already pushing to the max of what that hardware could do under DX. Basically, Y is faster so it's normal to be faster if the SW isn't holding her back to much and it DOESN'T mean that the new drivers are better than Mantle.
2nd - there is no "standard" point of reference to compare the SW since it's not running on the same HW and that's why you go back to the 1st point which makes "versus" standoffs a little bit pointless.
It would have been useful to see how these drivers increase apply to lower powered hardware or a little bit of disproportionate performance components mixed together.
Also food for thought, I can show 0% with Mantle or about 40-50% against DX, it's all about willingness to do that. How? Test the darn thing in a proper situation for which it caters! Same goes for nVIDIA drivers or any kind of testing.