Interestingly, several people hinted at the XMOS as the possible main CPU originally. I guess they'll be pretty chuffed to discover that they've got one anyway.
The stuff about the main CPU being secret but running at 1.6GHz in testing and being of "limited availability" and "you probably haven't even seen one in the wild" makes me wonder if it may be the pwrficient after all. If that's true, I'd love to know how they got hold of any.
http://en.wikipedia.org/wiki/Titan_%28microprocessor%29APM 83290 – The first implementations of the Titan core design. Two 1.5 GHz cores with FPU, 512 kB shared L2 cache, DDR2 controller, security engine, multi-channel DMA and I/O engine for gigabit Ethernet, PCIe, USB, RapidIO and/or SATA. It began sampling in October 2009
