I would not suggest upgrading now buddy.
Maxwell cards are coming out next year, and AMD is slashing prices big time for the imminent 8900 series
Your 7870 is a great card, and should give you good performance for the next 2-3 years on medium to high settings.
I'm kinda banging myself in the head for buying the GTX 700 series, should've waited for the price drop. 7990 are 670$ now!