If you're looking at a 7870, make sure you get a 7870 XT which is REALLY worth the money.
It's about the same performance as a 7950.
I bought a slightly used Sapphire HD 7950 boost on Amazon for $200 and I max out games like BF4, Sleeping dogs..
There's an R9 270x which is a rebranded 7870, or a r9 280x which is rebranded 7950/7970.
When comparing the 270x to the 280x, the 280x has a ~30% performance increase but ~$150 more.