Its unlikely best case scenario, GTX 1080 with GDDR5x oced gets 385 GB/s bandwidth.
GTX 1070 best case scenario with GDDR5 hits around 310-320 GB/s thats about 10 GB/s Bandwidth short of a reference 1080.
Looking at W1zzards review, of the MSI 1080 GDDR5x Gaming Plus a 5% clock speed bump and 10% higher memory resulted in a 7-11% performance gain.
Judging by the OC numbers the gains, Nvidia' GPUs on average still scale better with GPU clock than Memory clock. Considering the 1070 Ti features just shy of a 1080s core count and with an OC on the memory bringing it withing spitting distance of the 1080 as well. It goes without saying this 1070 Ti will function 98% like a GTX 1080 but for less money. Considering overclocked 1070s already rival or beat a stock 1080 this is pretty much a no brainer.
That said when Nvidia does stuff like this its the end of that GPU cycle. This model will have a shorter lifespan simply because new GPUs will replace it. While the 1070 and 1080 have been around for ages the 1070 Ti will be around for 6 months or so before we all hunker down and wait for the next gen.
On top of that due to the cut down nature of the GPU its likely making better use of defective dies instead of being a 1070 they can make a 1070Ti jack up the price and reuse defective dies and make a larger profit. They will likely let 1080 stock dry up while the 1070 Ti takes its place.