The S4 pro just isn't enough of an upgrade to get anyone excited. In terms of both features and performance the 600 scores a good deal higher. The S4 is just too close the the tegra (don't hate, look at the benchmarks). Even better if it's an 800 like a flagship deserves.
The S4 pro is a significant upgrade over the Tegra 3. The T3 was an overhyped chipset with less than impressive single thread performance, it was beaten by a load of chipsets announced later. In its defence the Tegra 3 is a very old chipset now. And the S4 pro thrashes it in benchmarks. Anyway the snapdragon 600 would obviously be a better choice since it is faster than the s4