There's a Supra in NOrth America putting 952 wheel horseower (minus drivetrain loss, probably about 1200) with stock internals. Granted that means everything else is not stock, but I haven't seen a Skyline do that yet. The guy drives it about once every two weeks. It retains all of the creatures comforts it came with.
There's less than 100 GT-Rs in north america so a comparison always ends u pas bench racing...anyway, "Ultimate" would be somewhat of an arbitrary definition since both cars tend to do th ings differently.
In Sport COmpact Magazine, a Supra and a Skyline are both in the Ultimate STreet Car Competition. The year before, a Viper won. Last year...I forgot.