The GTX 1070 is 57% 1440P performance gain over GTX 970. The RTX 2070 is ahead of the GTX 1070 reference-to-reference around 35% and 36% at 1440P and 4K, respectively.
The RTX 2070 Founders Edition is a vary capable card. It has decent overclocking potential, it runs quiet, and temperatures under load are acceptable. If we were looking at pricing similar to the outgoing GTX 1070, it would be an excellent upgrade. With no tangible benefits to be seen from ray tracing capabilities on these cards, no way you can test how feasible it is to run ray traced games on the entry-level RTX 2070, and no way to take advantage of DLSS, so you have to look at plain and simple GPU performance for gaming at 1440P, which offers the best value.
Unless you have future plans to run ray traced games, the GTX 1070 Ti would offer the best value,.. with RTX 2070 being priced at between $499 and $599.