I'm doubtful of this as the GP edition of the GS4 and touchwiz version have pretty much the same benchmarks and perform almost identical.
Disassembly of the Samsung firmware actually shows the coding tags Samsung put in place to detect benchmarking apps and crank up the CPU accordingly just for those. Not sure if this is at all impacted by Touchwiz....if I were coding it, I'd put it at the firmware level.