I have my doubts about 3070 beating 2080ti. Could be similar which itself will be amazing for its price. From Toms Hardware:
The RTX 3070 should still be plenty fast for 1440p gaming, and more than fast enough for 1080p — just like the RTX 2080 Ti. Nvidia says it will perform "better than the 2080 Ti," though we take that marketing-speak with a scoop of salt. Out of all the benchmarks we ran, there was only one (Doom Eternal) where the 3080 actually doubled the 2080's performance.
Anyway, saving $200 and buying a 3070 could make a lot of sense. It's interesting to note that the RTX 3070 is a substantial step down from the RTX 3080, however. The 3080 has 48% more GPU, RT, and Tensor cores, it has 20% more memory, and the memory is clocked 36% higher. That's a big enough gap that we could see an RTX 3070 Ti down the road, but at what price? Alternatively, wait and see what AMD's Navi 2x / RX 6000 GPUs can do, which we'll hear about more on October 28.