Im also reading from multiple credible sources that the boss is underrated to avoid stepping on any GT500 toes. 444 is apparently wrong, and its closer to 460. Just what im seeing based on some early dyno tests from folks who would know.
Could also be that it just has less of a loss than folks are used to through the drivetrain, maybe that new 6 speed is just really efficient?
I do think there is something to be said for the traction issue brodom is referencing. If you put them both on tire id bet the GT500 pulls out some.