Let me sort this out.
Stacking GPU cards into SLI or XFire configurations yields better framerates at a given graphics setting. That is ALL they do. It allows the cards to share the work of creating individual image frames and displaying them.
Buying a GPU with more memory (3GB vs 1.5GB, for example) will allow the graphics card to put together bigger (more detailed, higher resolution) images before they are displayed onscreen and maintain the same FPS, all other factors staying constant.
No matter the number of GPUs you run in unison, they will never make up performance losses when the images they are collectively producing are scraping the bottom of their memory bank. At 1920 x 1200, 1.5GB cards in SLI is JUST enough in more recent, graphically demanding titles, and I regret not waiting and getting two 3GBers, because demands of future games are just gonna be greater.
So, what in the name of God are these people on about with "SLI is overkill"? It may be overkill for World of Tanks or Minecraft, but most of us play more games than DX9 MMOs and the like. If you think higher (smoother, better) rates of performance are "pointless" then yes, a GTX 580 SLI setup is pointless. But if you want more frames per second onscreen, then it is not. It's like these people sit down in front of an SLI system running like that and think to themselves "Naw, yeah this gameplay is way too smooth and doesn't stutter or anything, total overkill."
Like, come on. A GTX 580 SLI system, like mine, is pushed to its limit on games like The Witcher 2 and the BF 3 beta. These games and the games VERY soon to come in the near future do and will make very efficient and full use of the available GPU computing power. The only way this would be overkill is if it did not in any way benefit performance, and, infact, had a detrimental impact on the gaming experience. There is no such thing as "too smooth" or "too high quality" when it comes to PC games IMHO, because I can't fathom spending the time and money we do on our machines if we didn't demand the absolute best possible gaming experience.
i see my fps drop to 40 at times in the bf3 beta and that to me is very noticeable. this is all on ultra and at 1080p
since SLI is the obvious solution, when kepler is released, how much of a price drop on the current 580's is expected? i haven't been around long enough for a gpu refresh
/not a hijack