[citation][nom]orwellswift[/nom]To me the difference in performance, not really being all that much either way, is quite substantial when comparing them at a design/ architectural standpoint. To use an analogy to exemplify my idea, let's say that the gtx-680 is a Mercedes and the 7970 is a Ferrari. Negating the price difference between the two and simply looking at performance, the specs for the Ferrari should always outperform the specs for the Mercedes. The Ferrari/ 7970 having 4.3 billion transistors, a 384 bit bus, and 3GB of memory and the Mercedes/ gtx-680 having 3.5 billion transistors, 256 bit bus, and 2GB of memory. Certainly the Ferrari/ 7970 is more of a high-end beast than the Mercedes/ gtx-680 which makes you wonder how a lower performing product can keep a marginal gain on the competition, especially when you figure that the 7970 has had three months market time to solve consumer driver issues which the 680 is basically tuned to reference drivers. To use the car analogy again, the Ferrari most likely cost a lot more to develope and produce than the simpler Mercedes since the Ferrari is a lot more complex in design, therefore the profit margins for the Ferrari will be a lot less than the Mercedes. Literally meaning that Ferrari can only sell cars at a limited and high price point where as at the moment since the Mercedes/ gtx-680 can outperform the Ferrari/ 7970 and Mercedes can upsale their car at the same price point for a much higher profit therefore creating a distinct edge in price competition. The analogy used is only to illustrate the spec differences between the two cards, in the real world a Ferrari will generaly be far more expensive and always outperform a mercedes, I only use these cars as an example because they are both high-end luxury cars that really don't compete in the real world but in the case of the gtx-680 and 7970, one card should vastly outperform the other but doesn't. I am by no means an expert on graphics cards and this is just my way of interpreting the results of endless hours of professional tests and benchmarks. After initially reading the review I had a mental picture of a guy on a moped with a bumper sticker that said "eat my dust" with a guy on a Harley right behind him.[/citation]
Sorry, but it doesn't work that way. How many transistors a chip has does not define performance (it never has) exactly, how wide it's memory interface does not define performance exactly, how much memory capacity they have does not define performance exactly. There are huge differences and factors that you ignored because you don't know what you're talking about. I'm no expert, but I think I can try to clarify a little more.
Kepler seems to have greater gaming performance per core than GCN if a 1536 core chip clocked at between about 1GHz and 1.056GHz beats a 2040 core chip clocked at 925MHz. Kepler is obviously inferior to GCN for SP floating point performance (DP is artificially lowered by Nvidia, not low because of problems with the chip so I won't go into it right now) because even though the 680 is a higher performing card at stock than a stock 7970 for most games, the 7970 has a huge lead in SP computational performance. However, the SP performance advantage of the 7970 seems to be rather similar to it's core count advantage, so the Kepler and GCN cores probably have similar computational performance.
The 680 has less efficient AA performance for most of the titles than the 7970. This is likely because of it's memory bandwidth bottleneck. Of course, it's performance lead is enough to not let the 7970 retake the crown at stock frequencies, but it shows promise for the 7970 when overclocked without being held back by the current version of Catalyst.
The 7970 has a big VRAM capacity advantage of 50% too. That usually won't matter for most setups until you hit things like Eyefinity resolutions and such, but it may become more important in the future, especially with future-proofing. If two 680s or 7970s are necessary for 2560x1600 in some new games in a few years, well then you can bet that a mere 2GB of memory might become a problem. There's a reason that AMD mostly uses 2GB for their 6900/6800/7800 only, not their even faster 7900 cards. However, Nvidia seems to really like skimping on VRAM capacity as you can see them do it with multiple cards, not just the 680. The 570 only has a mere 1.25GB, limiting going far over even 1080p. The GTX 580 isn't much better with only 1.5GB of VRAM, but plenty 580s have 3GB so it's a little different whereas only one or two 570s has 2.5GB.
The 7970, when overclocked past Catalyst's limits to about 1300MHz, will be roughly similar to the 680. All the 7970 needs to compete with the 680 in performance is for Catalyst to stop limiting overclocks to 1125MHz. Better drivers for both cards will come, then we will see if either card is truly the better. As of right now, it seems like the 680 is more power efficient. However, we have yet to see the 7970 here on Tom's compared against the 680 when both are truly overclocked to their reasonable limits. The 7970 obviously has a lot more performance headroom, but the 680 seems to have hit a cliff in performance almost out of the box.