i’m not an expert, but i’m pretty sure only a select few games support SLI, which is why you’re only seeing one card being used.

https://www.pcgamingwiki.com/wiki/List_of_games_that_support_SLI

^ here is a list you can reference.

i’m going through something similar. wanting to upgrade, not having enough time to justify it. like me, you’re going to need a whole new mobo, new processor, new ram, new power supply all to accommodate the new GPU. the question for me was, why buy a 3070 if my motherboard doesn’t have PCIe5 support?

just some things to consider. if you enjoy building, then do it. PC gaming is a fun, but expensive hobby. do what is best for you. your 1070 is probably doing just fine for your needs right now.