Even excluding the 1-foot rollout (0.3s) will require 443 hp for an AWD car to do a ¼-mile in 12.6s, and that's with a manual or conventional automatic transmission. Although I will argue that the R34 V-Spec can possibly trap 112 mph.
Just because they claim it's "stock" doesn't make it one. #WolfInSheepsClothing
This 12.3 figure is not inaccurate, but very optimistic. It's like the Dodge Hellcat twins and their 10-to-11-second quarter-mile times. The R34 GT-R slots between a 996 Carrera 4S and a 996 Turbo in overall performance.