Don't put too much heart into the increased maximum clocks of the S600 implementation for the GS4 when compared to other smartphones with the "normal" S600.
Real world results are pointing to the GS4 having very similar performance to the HTC One, which has lower max clocks for the GPU and much lower memory bandwidth.
The S600 in the GS4 probably has more aggressive underclock throttling for thermals and power consumption, to compensate for the higher max clocks.
A little trip to GLBenchmark (Median scores, which will show stock clocks) or 3dmark online results will show that the HTC One is some 4% slower than the GS4 even though it uses older drivers. Then the Exynos 5410 trails behind both of those S600 solutions by more than that:
GS4 Exynos 5410: 699 Frames
GS4 S600: 859 Frames
HTC One S600: 825 Frames
So Samsung may start to ramp up the production of the GT9500 while building more Exynos 5410, but they will be releasing devices with slower GPUs in the process.