ConclusionWith this first Kepler generation GPU, the GK104, NVIDIA's main objective was to revisit as far as possible the overly weak energy yield on the Fermi generation, which was probably becoming increasingly difficult to manage. This objective has successfully been attained, and represents a hugely important development allowing NVIDIA to market more efficient products.
In the course of developing this GPU, which was originally designed for the slightly lower performance segment, it became clear that it might be able to compete with the AMD high end. NVIDIA made sure that this was the case by preparing a GeForce GTX 680 with high clocks and reworked drivers as well as the in-house turbo technology, GPU Boost, which gives a little additional performance and just enough to outperform the Radeon HD 7970 in our set of games.
While the GeForce GTX 680 retakes the crown as the highest performance mono-GPU graphics card currently on the market, it only has a slight advantage and its performance is very variable from one situation to another. The card suffers particularly with 8x antialiasing, which puts a lot of demands on memory bandwidth.
On top of this, NVIDIA has categorically refused to go into any detail in terms of the specifics of how GPU Boost will work on the cards that we'll find in stores. It has to be said that the technology, unlike turbo on CPUs, is not deterministic and that any two samples of the same card will therefore perform differently. Our tests have shown that GPU Boost gave a performance gain of between 4 and 5% on a sample that we imagine was carefully chosen by NVIDIA and tested under ideal conditions. Therefore we can only conclude that this 4 or 5% spread is the range of performance that GeForce GTX 680s will give once in your system and that the performance of these cards could therefore be very close to that on the Radeon HD 7970.
In terms of overclocking, the GK104 has less extra potential than the Radeon HD 7900s as GPU Boost already uses much of this potential. Memory overclocking can however go much further and can give a real fillip to the GeForce GTX 680s which are somewhat lacking in memory bandwidth, providing a nice gain in performance particularly in situations where these cards don’t do so well. In order to outperform these boosted GTX 680s, the Radeon HD 7970 will have to be massively overclocked, with increased GPU voltage and higher noise levels.
With the same pricing of around €500, it's not fully obvious to separate these two graphics cards, especially as NVIDIA’s addition of support for four screens removes AMD’s Eyefinity advantage from the balance. When all’s said and done, the Radeon HD 7970 retains an advantage in terms of standby energy consumption and this may well make the difference for some usages. Its architecture also looks towards the future when it comes to GPU computing and full DirectX 11.1 support. Nevertheless, our preference tends to be for the GeForce GTX 680, which enjoys a slightly better energy yield, slightly lower noise levels, gives access to the 3D Vision ecosystem, the most common for 3D stereo, has drivers offering innovative features such as adaptive v-sync and in general provides optimum support for new games more rapidly. In general but not always as the Alan Wake results for GeForces show.
It also has to be said that neither the GTX 680 nor the HD 7970 offer particularly good bang for your buck as AMD and NVIDIA have settled for doing the strict minimum in terms of pricing efforts, helped as they are by the low availability of 28nm solutions, which is currently stopping competition from kicking in fully. How much of an advantage the two solutions give is also debatable. For playing at 1920x1080 for example, the Radeon HD 7870 will very often do fine if you’re willing to accept a few compromises in terms of your graphics settings in the most demanding games. On the other hand, a GTX 680/HD 7970 mono-GPU solution won't give enough power for gaming in surround at high settings, in which case you're forced to go for a multi-GPU system… though you will of course need to make sure that your multi-GPU doesn't suffer from any micro-stuttering!