Have a read of
www.guru3d.com or
www.techreport.com which have some nice breakdowns of the ins and outs of SLI and Crossfire because it will save you time and help you gain a better understanding.
SLI will only improve where there is room for improvement. At 1280x1024, a modern CPU can keep up with the graphics card in that it can shift a game's wireframes around quickly enough to keep high minimum frame rates (i.e. stop the graphics card from spinning its wheels, as such).
Also, the texture demands at such a resolution aren't as high as at 1600x1200 or higher, therefore most mid-range graphics cards have enough pixel-shading power to do the busines.s It's only at higher resolutions where single graphics cards tend to struggle that SLI adds any notable benefit because of the added horsepower, memory, etc.
Besides, if one can get a minimum of 60fps at 1280x1024 with high IQ, what's the point in more graphics card oomph? SLI can potentially improve upon it, but there would not be any noticeable difference.
At 2560x1600, the minimum frame rate may be down at around 20fps; assuming the game is not CPU limited, adding a second card will shift that up to a maximum of 40fps, instantly making the game more playable.
And please, make sure your spelling and grammar make sense because your post is otherwise pretty difficult to decipher.
