As of now, for Radeon cards the thousands place denotes the series and the hundreds and tens place denotes the performance category.
(The X's are digit placeholders for specific model numbers)
For a gaming rig you would probably want to have a 77XX or better.
For performance gaming go for a 78XX or better.
For a high performance experience get a 79XX.
For extreme performance look towards the 7990 which is a dual gpu card.
NVIDA cards are numbered in a very similar fashion.
It sounds like you are willing to drop some cash so look towards the higher end if you want a nice buffer.
AMD's new series of Radeons is supposedly scheduled for the final quarter of 2013 or early 2014 so if you can hold off maybe you could snag the flagship model (usually numbered X970) when it comes out.
Beware that waiting for the next release will result in paying a premium cost for the hardware and usually having to use newer graphics card drivers that haven't been heavily tested by the community yet. If I remember correctly, Linux drivers for the 7970 didn't exist on launch-day.
If you are looking to buy a card right now and want to have a big buffer go for the 7970. If you want to spend a bit less cash look to the 7950 or 7870.
Hey nice. That is look very great. Thank you, so I can imagine this section a lil bit better. So the 7970 is close to GeForce Titan. But 7950s looks very attractive.