I have tested both on FP evogreen. The HKS allows for 2 bar boost at 3500 rpm without surge and goes onto support 2.3 bar @ 3800-3900 rpm. The GSC S1 similar to stock cannot support that much boost without surging the turbo. 2 bar boost at 4000-4200 rpm without surge.

All tests in 3rd gear for full boost.
5th gear tested for surge.