People probably should stop using "PR metrics" from MS's marketing slides and "performance estimates" given to insiders as a baseline of Durango's performance.
From a pure numbers angle Durango is *not* 6-8x faster. Architecture aside: Fillrate is about 3x (4 vs. 12.8Gpixels), texturing is about 5x (8 vs. 38Gtexels), flops are about 5x (240 vs. 1200GFlops), about 3x triangles (500M vs. 1600M triangles/sec), aggregate bandwidth, counting only the bandwidth to the eDRAM and not the internal bandwidth is something less than 4x (54 vs. 170GB/s). Memory footprint is over 6-8x jump, once you count count the OS it is about 10x.
Durango is mostly in the 3x-5x range of raw peak performance improvement range.
Before the numbers are poo-poo'd with "efficiency of modern GPUs" I would note that Durango also has to perform at 1080p, counter diminishing returns, GPU performance doesn't necessarily increase linearly with raw specs (i.e. workflow issues), more expensive shaders to get better results, etc balance that out--especially the higher resolutions. So any appeal to "it will look 6-8x better" (whatever THAT means) is easily then cut in half but increasing resolution, which brings it back inline with 3x-5x or less in terms of "realized" potential.
The good news is Cape Verde seems quite capable of playing games like BF3, Batman AC, Dirt 3, etc at relatively high settings (minus AA) near 1080p at 30Hz so indeed Durango can play this generations worth of content the way mid-low range PCs currently do.