Because I said I was going to, attached below is a datasheet for GDDR5 from Hynix
http://www.hynix.com/datasheet/pdf/graphics/H5GQ1H24AFR(Rev1.0).pdf
Page 43 gives the CAS timings for GDDR5 at various speeds. At 5.5 GT/s its CAS setting is 16, which at 1.375 GHz command clock rate gives a ns latency of 11.6ns.
From the teardown by iFixIt, the Xbox One has 8GB of H5TQ4G63AFR DDR3-2166. From the H5TQ4G63AFR datasheet (http://www.skhynix.com/inc/pdfDownload.jsp?path=/datasheet/pdf/dram/Computing_DDR3_H5TQ4G4(8_6)3AFR(Rev1.0).pdf), at 2166MT/s (1066.67 GHz command clock) its CAS setting is 14, which gives a ns latency of 13.1ns, slightly higher than the PS4.
For the usual DDR3-1600 that most PC's ship with, the average CAS timings is between 7-9, which at 800 MHz command clock gives a ns latency of 8.75 - 11.25ns, slightly better to on par with GDDR5 (so I was wrong about GDDR5 being less latency). But the difference isn't as large as some people make it out to be, and in the case of the Xbox One (which isn't part of this discussion I know but for completeness sake), GDDR5 in the PS4 actually has lower latency than the DDR3 in the Xbox One (obviously the ESRAM mitigates this to a degree).
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