Is $80-90 a good price for one of these? How would two of these compare to the new 980?
Here's a direct comparison on a very reputable and underrated bench-marking site. You can also visit here to see every graphics card's scores (pretty much every single one ever).
Honestly, they don't really compare. Around a $100 would be a great deal if you can get it, but you shouldn't expect to put the cards head to head, the 980 will win any day, but at about half as powerful, the 590 would put up a good fight. As far as 2 of them, it's kind of luck of the draw as to what games can utilize multiple cards correctly. You might get comparable performance out of some games, but others, you might as well forget the fact the you've even got SLI.
I always thought the larger memory bus would be a benefit and as such at the very least perform a tad better in graphical editing utilities but the 980 would run circles around one in gaming.
Its too old of a card to be worth it in my opinion. A r9 290 gtx 970 or 980 are much better buys then a neglected older card.