If you put the exact same turbo setup and ran the exact same boost level on stock LS and stock GSR motors, the GSR would make more power.

The more aggressive cam profile that VTEC uses for high RPM helps any motor, regardless of whether it's normally aspirated or running forced induction. The GSR cylinder head also flows much better numbers, and the high compression ratio produces more power (it won't detonate as long as there's proper tuning).