First off, I know I can get a better performance to price ratio by doing SLI, but for some unkown reason, I don't like the look of two cards in one system. Now that that is out of the way, I currently can't decide between the 690 and the 7990. I know the 690 is better for Adobe products, which I use, but Adobe and AMD recently came out saying that they are working on having OpenCL work with Adobe for GPU acceleration. I also know that the 7990 should have a higher frame rate since it has two 7970 GHz editions unlike the 690 using underclocked 680's. By that, it seems the 7990 should be the better option, but what keeps turning me away from it is all the things I read about the AMD line of GPU's having inconsistent performance. I have read about it having a higher fps, but at an incosistant rate. I.E. it will have lower lows, but higher highs. Does this still apply today, or has this problem been solved by now?
Per usual, there is more than just performance, i.e. framerates, when determining the "best" platform for gaming. We of course speak about the real-world "feel" of gaming between SLI and CrossFireX on a multi-display setup. There is no question that SLI feels smoother, thanks to the added technology that NVIDIA employs to address this very topic. That said, you can still have a good experience with AMD CrossFireX in Eyefinity given enough framerates. In those terms, this is where AMD CrossFireX has excelled today in our testing.
I'll chime in on the inconsistent performance. I think what you're referring to is micro stuttering and frame latency. There's a thorough description of it here: http://www.anandtech.com/show/6862/fcat-the-evolution-o... and in articles linked from that page.
As I understand it, the issue is to do with how consistently frames are displayed. To take an extreme (and well beyond real-world) example, a video card could take just under a second to process one really complex frame and then manage a further 59 frames in a fraction of a second. An FPS count would have the card displaying 60 frames per second, while the user experience would be anything but smooth.
Neither AMD nor Nvidia are immune to the issues even in single card setups, but multi-card setups are where issues become more noticeable for many. I think it's widely agreed (and proven) that AMD are certainly behind Nvidia here, though recent driver releases have closed the gap (which was embarrassingly large to begin with). How much people notice, or are bothered seems to vary massively between people. Hope this is helpful?
I think otherwise, you'll get a bit better performance out of a 7990, at the cost of heat and noise.
According to this: http://www.anandtech.com/show/6881/opencl-support-comin... you'll need to get the next (yet to be released) version of Premiere Pro to get OpenCL support.