An i/h/e GSR is about 10 whp short of a stock ITR. Slap i/h/e on an ITR and the gap widens again.
If you took an i/h/e GSR motor and put in some cams that are hotter than ITR cams (skunk2 Stage 2, JUN Type-III, Toda Spec B) you'd probably top the output of an ITR.