I'm pretty sure the GTX 1070 throttles around 84C, so you are fine. There is nothing wrong with running GPUs at their max temperature. People have mining rigs that are running their chips at high temps 24/7 for years without a problem. Rarely is the actual silicon dying a concern, the stuff that is way more likely to die on a graphics card are the memory modules, the VRM, or the fan(s). Cooling those three things is more important than cooling the actual GPU chip.