Versions of Tegra 4?

I apologize for posting this simple question in this forum as I’m not a developer. This seems like the only place to get relevant information, and this thread seems to be the only active one.

The Tegra 4 used in the Nvidia Shield is rated at 1.9 GHz, the same rating as the Tegra 4 used in the new ASUS Transformer TF701T. But, the Tegra 4 used in the new Microsoft Surface 2 is rated at 1.7 GHz, and the Tegra 4 used in the new HP SlateBook x2 is rated at 1.8 GHz.

According to Nvidia they only have two versions available, the Tegra 4 and the Tegra 4i. So, what are the other specs on the other chips?

Thanks_Dennis