>>361475019
I don't know the performance differences much, but if you already have a 1080 and are going to upgrade to just a 1660 6GB, wouldn't that be... a super mini increase? 
Might as well wait for the 3060 restocking then, for the upgrade to be worth it at least a little bit. Plus, the 3060s have a lot more VRAM. 

When I bought PC parts 2 months ago, 3060s were in stock quite often. Then again, the Christmas season is coming up and people are still at home much more due to COVID, and the supply chain issues remain as well.