If you compare two different cars for the aim of having an honest comparison about the turbos, you HAVE to factor in all the other differing mods done to the cars. Hell, something as small as one person having new APEXi pods and the other one dirty HKS pods can produce as much as 5rwkw difference, let alone cams, throttle bodies, head work, ECU tuning, engine compression, etc etc etc...
Those kinds of comparisons are fine for good fun (like we're doing down in Melbourne in a few months re: GTR low mount turbo choices), but it's hardly a scientific comparison.