Found a 4870x2 for $60 locally; what are your opinions on older tech such as this?
I'm really trying to stay below $100......
4870x2 is somewhere between a 7790 and a 7850 in performance, on average. Crossfire has some disadvantages though, such as only working when fullscreen and not scaling in some titles (though you'll find most do work, and well). $60 is a bargain for the performance, but you don't have DX11, and it will run loud, hot, and draw a lot of power. You can't really Crossfire it with your current 4870 for TriFire as your current card is only 512MB - it would hurt more than it helps.
At $100, the 7790 is your best bet for a new card. A GTX460 isn't bad but at the same price I'd take a 7790 over it - spring for it if you can find one under $75.
Can you raise your budget a bit if you take into account selling your 4870? It's still worth $40-50. That would put you solidly into HD7850 territory, which currently holds the crown for priceerformance.