4070 or 6800XT? Upgrade CPU or nay?

Hi guys! So I'm considering upgrading my...veteran PC. Currently, a Core i7 6700 with an Nvidia GTX1070, 16GB RAM running from a Gigabyte Z170 Gaming K3 (PCIe 3.0) mobo. I'm currently considering to upgrade the GPU to a 6800XT, although I saw the 4070 for a bit cheaper, maybe ~80USD less. I've posted this earlier, and got a helpful reply making me aware both of these cards are already PCIe 4.0, and while the CPU might be a bit bottlenecked, it should be a noticeable performance increase. I've got an additional comment saying otherwise, that even currently with the 1070 the CPU would be bottlenecking. I was not able to reply to these, as my post (on FOSS gaming community) was removed. I guess this is not FOSS enough... So, PCMasterrace, what do you guys think?

Additionally, this veteran mobo would support a slight CPU increase to a 7700, which on the second hand market it wouldn't be all that much money (for what I reckon, not that much performance increase, either). What do you guys think? What should I do?

Thanks!