Sounds like Durango's "secret sauce" lies within it's blitter (aka: 4x data move engines). If they can have a comparable amount of bandwidth between RAM and GPU while simultaneously doubling the RAM then that can become an area of exploitation by devs.
From: http://www.eurogamer.net/articles/df-hardware-next-gen-xbox-specs-leak
"In the case of Durango, the CPU is married up with 8GB of DDR3 memory, working in concert with 32MB of what is dubbed "ESRAM" - fast work RAM connected directly to the GPU. The two pools of memory operate in parallel, and while we haven't confirmed overall bandwidth, the leak's 170GB/s throughput certainly seems plausible. Also interesting about the RAM set-up is that the ESRAM isn't merely connected to the graphics core as is the case with the Xbox 360's 10MB of eDRAM - in Durango, it's hooked up to the northbridge (the interconnect between all major internal components), meaning it offers general access to other components in addition to the graphics core."
And that above statement didn't even take into account the 4x data move engines, which they later on go on to claim to know very little as to how it works. One thing I'm certain of is that purely reading spec numbers from a paper is not going to cut it anymore.