OK, here's the logic. Tegra 4 is based on A15. Tegra 3 is based on A9. A15 is ~40% faster than A9 clock-for-clock, so we know tegra 4 is going to be faster than 3, assume 40% (cpu-wise). But the current S4 pro/Krait is already as fast as A15-based systems. It was shown already that Tegra 4 won't be clocked much different than 3 (1.9ghz vs. 1.6ghz max). That's great except the currently-available Krait is already as fast as A15-based systems. Ergo, the current competitor's chips are already as fast as tegra 4, except T4 won't launch in products until 6 months from now. Qualcomm has already announced their successors to the S4 pro (nomenclature changes aside), which they claim to continue their performance improvements over the previous generation (we can take that with a grain of salt; every manufacturer likes to say this about next-gen releases).
However you break it down, Tegra 4 will be using an outdated cpu platform when it goes live. That's not to say that their claims of "six times the graphical capabilities" of Tegra 3 can't be useful, but it's a sad fact of the matter that for being released into the wild six months from now, T4 won't be using a very current cpu platform. It'll only be catching up to what is already available right now.