From /usr/share/doc/xorg-x11-drv-nvidia-*/README.txt:
Quote:
The NVIDIA Accelerated Linux Graphics Driver and NVIDIA GPU-based graphics
cards support resolutions up to 8192x8192 pixels for the GeForce 8 series and
above, and up to 4096x4096 pixels for the GeForce 7 series and below, though
the maximum resolution your system can support is also limited by the amount
of video memory (see USEFUL FORMULAS for details) and the maximum supported
resolution of your display device (monitor/flat panel/television).