Durango has always had 8 gigs GDDR5, sony matched specs

[theprof00]

Ps4 has 8gb of gddr5 because the apu strength increases dramatically with it.
Nextbox has no reason to use gddr5.
Dev kits showed 8gb ddr3 with 512esram, which is a completely different way to enhance the power of the system.
Ie; for ms, the ESRAM is their gddr5...its just not as good, but cheaper indeed.