No, you cannot SLI those 2 different GPU models. Though, without SLI, even if you use the card for some other purpose, there is no point in having 2 cards on one system, IMO. It will just draw extra power as well.
Which PSU model/brand is that though? Use the RTX 2060 instead.
I want to use 1060 3gb for octane render 3.06 but i don't have octane 4 for 2060Yes, you can use one at a time.
That's the kind of setup most people have.
Just use the more powerful GPU and sell the other.
3 GB GTX 1060 is also a good GPU for 1080p gaming but at the highest settings, it's VRAM could become a limitation.