You're correct Achim. The 2560 by 1600 limit is simply the wording of the marketing dept at Nvidia. In reality a DVI-D output is limited by it's 300Mhz clock. 2560x1600x60hz = 245,760,000. So even there is some room to grow. Assuming you have a device that can read it, any width/height/fps combo can be used (up to the max texture width/height supported by the card). You can get higher resolutions if you reduce the refresh rate of the output. I've done 7680x1080x30hz before.
I haven't tried but I wouldn't be surprised if DisplayPort outputs could do even more since they have a higher possible pixel clock.
So it's not limited by the card, simply the specification of the cables you are using.
Remember if you are going from a DisplayPort output to DVI at higher than 150mhz (DualLink DVI) via a dongle you need to use an Active DisplayPort converter with a USB power:http://store.nvidia.com/DRHM/store?Acti ... =227587600