I recommend you to get vega 64 instead of RTX 2060 or 1070ti, as the performance of vega 64 is slighty better than the both card and you will get it for lower price than RTX 2060 and 1070ti
Here is the part list i will suggest you
AMD - Ryzen 5 2600X 3.6 GHz 6-Core Processor
Cooler Master - MasterLiquid ML240L RGB 66.7 CFM Liquid CPU Cooler
Gigabyte - X470 AORUS ULTRA GAMING ATX AM4 Motherboard
MSI - GeForce RTX 2070 8 GB VENTUS Video Card
EVGA - 750 W 80+ Gold Certified...
2080 will be the better choice if you really want to see a noticeable difference ein performance, also you can go with 1080ti. But upgrading to 2070 will not make a huge performance difference.
Most of the miner overclocks there GPU to mine as much as they can. So a miner hadn't overclocked there GPU it's like a myth. But if you are getting a good deal then you can definitely consider it but check it properly before buying