Overclock3D claims the new card will be equipped with GDDR5 memory clocked at 9GHz effective. That's 1GHz more than the GeForce GTX 1070, although it should be noted that some GTX 1060 6GB cards are already shipping with 9GHz GDDR5.
From what we now know, the GTX 1070 Ti will be a lot closer in performance to the GTX 1080 than the GTX 1070. Compared with previous generations, there was a big performance gap between these two cards so the GTX 1070 Ti is a natural fit.
The new variant will have almost as many SMs as the GTX 1080 (38 vs 40) and will have the same base clockspeed. The Boost clockspeed will 50MHz lower though, and as outlined above, the memory will be less potent too.
NVIDIA is reportedly planning to launch the GTX 1070 Ti on October 26. These plans can always change but at the moment this whisper is that NVIDIA is targeting a MSRP of $429.