ok, playback is fine. But what about the GPGPU performance of these things?
I se comparisons to W9000 cards and 2 of those would cost more than the new MP!
However, when you compare W9000 (released Aug 2012

) to a new card, say R9 290X (released Oct 2013) you get:
card: R9 290X - W9000
core speed: 1000 MHz vs 975 MHz
memory: 4096MB vs 6144 MB
memory speed: 1250 MHz vs 1375MHz
memory bus: 512 Bit vs 384 Bit
memory bandwidth: 320GB/s vs 264GB/s
shader units: 2816 vs 2048
shader performance: 1830.4 vs 1331.2
OpenGL: 4.3 vs 4.2
so except for memory size, I call R9 290X the winner. Where do the D300, D500 and D700 stack up? As many have pointed out, they are not (at least not easily/cheaply) upgradeable so the choice become important to the people considering the new MP. Sure the new MP has two but still.