Maximum resolution on external displays
This page list the maximum resolution you can get on an external display. Annoyingly, the official information is known to be incorrect in some cases. Please update with your info.
Output via the analog VGA port is always limited to 2048x1536. This is a rather square aspect ratio. On modern monitors 1920x1200 is more likely the maximum.
Known configurations to work and not to work at 2560x1600
T61p with Advanced Mini Dock