I am afraid it's not so much the CPU as the code still being unoptimized. I've gor the QX6700, and cannot play full framerate, either - the CPU usage is just 10-15% !!!
Also, when rendering the CPU usage never exceeds 40% with 32 bit floater on, which sucks! Actually, the playback is not multi-threaded at all - it's exactly the same whether I set 1 thread or all 4.
I think everybody would benefit if we all report our maximum playback quality setting, yielding watchable frame rate with 32bit enabled, along with the CPU used. Here I go (25psf project):