AMD came storming out first, but in the end it was NVIDIA who seized the peformance crown with its GeForce GTX 680 Kepler GPU. And that's where the story might have ended, had AMD not said "not so fast."
AMD countered with a specially binned Radeon HD 7970 "Gigahertz Edition" (GE). The new card is essentially the exact same as the original Radeon HD 7970, which shipped at the end of January. But it does bump the core clock from 925 MHz up to 1000 MHz (hence the GHZ part) and the memory clock from 5.5 GHz to 6 GHz.
But the majority of the gains come from a new set of drivers that in some ways mirror NVIDIA's Kepler drivers, by providing a "Boost" mode. Unlike the Kepler drivers, AMD locks the cards into a solid maximum clock -- 1050 GHz -- which is sort of nice, given that you know what you're getting. This contrasts with NVIDIA which guarantees a minimum boost clock, but whose maximum boost clock is somewhat random depending on chip quality -- essentially luck of the draw.
That's all fine and good, but the compelling question is whether the Gigahertz Edition was worth alerting the press and claiming to steal NVIDIA's thunder. Well it turns out it does provide a significant boost over the base model, enough to put it in contention once more for the graphics crown.
The card trades blows with the Geforce GTX 680 in AnandTech's testing, with neither card managing a convincing victory. The only a couple of areas where one card clearly wins. One is the multi-monitor tests, where AMD's card is the clear winner. But in power, noise, and heat, NVIDIA's card clearly wins.
The most important issue thus becomes price. Both the GTX 680 and new HD 7970 GE are $500 USD. Thus the graphics races is essentially a dead heat.
Moving down the ladder AMD offers the base HD 7970 for $430 USD. For $30 USD less NVIDIA offers the $400 USD GTX 670 -- which predictably has a bit less performance than HD 7970. Then there's AMD's HD 7950 at $360, which is in turn a bit lower performance than the GTX 670.
In other words, smart pricing from both companies means that the best card for you in this round of the graphics war depends on which price point you're looking at. At the points occupied by AMD, AMD wins, at the points occupied by NVIDIA, NVIDIA wins. But at the top there's now no longer a clear winner.