Let’s get an overview of the performance of the new card by means of summary diagrams. The first pair of diagrams compares the AMD Radeon HD 7970 and the Radeon HD 6970 at their default clock rates, the latter card serving as the baseline.
As you can see, the new card brings about consistent improvements in performance across most of our benchmarks. It is 39.6 and 43.9% ahead of the HD 7970 in the MSAA-less mode and 33.7-30.7% faster with MSAA at resolutions of 1920x1080 and 2560x1600, respectively. It is easy to see that the Radeon HD 7970 enjoys a larger advantage over its predecessor with MSAA turned off, although its 384-bit memory bus and larger amount of onboard memory should be more beneficial in the heavier mode. We could try to explain this by imperfect drivers if this behavior were not so consistent through most of our tests.
The second pair of summary diagrams compare the AMD Radeon HD 7970 3GB with the previous single-processor king GeForce GTX 580 3GB, the latter serving as the baseline.
The GeForce GTX 580 is still faster in StarCraft II: Wings of Liberty, Tom Clancy's H.A.W.X. 2 and (at one resolution only) in Hard Reset Demo but the rest of the tests are won by the Radeon HD 7970. The new card’s advantage is enormous in such games as Total War: Shogun 2, Sid Meier's Civilization V and Just Cause 2 and averages 17.1-19.7% at 1920x1080 and 20.2-28/2% at 2560?1600 across all the tests. If the GeForce GTX 580 3GB is overclocked to 910/1820/4780 MHz, the gap shrinks to 1-5.2% at 1920?1080 and 0.8-10.6% at 2560?1600:
So, if you’ve got a well-overclocked GTX 580, you shouldn’t worry about upgrading.
On the other hand, the Radeon HD 7970 3GB is itself a splendid overclocker. The next pair of diagrams shows the performance benefits from our overclocking it from its default 925/5500 MHz to 1130/7000 MHz.
The average performance gain is 18.6-23.5% at 1920?1080 and 20-22.5% at 2560?1600. If measured in percent, the frequency growth of our sample of the card was 22.2% for the GPU (from 925 to 1130 MHz) and 27.3% for the memory (from 5500 to 7000 MHz). Thus, the Radeon HD 7970's performance increases almost proportionally to its clock rate, which is good news for all overclockers.
Here is a table with the detailed test results for your reference: