Take a look at this. It may fix the 1680x1050 issue for some.
Users may be unable to use the native resolution of some displays when using Intel chipset graphics. Resolutions such as 1680x1050 and 1440x900 are not available in graphics properties.
The display EDID is not read properly when connecting to a subset of Digital Flat Panel (DFP) displays.
Intel has released this driver to specifically address this issue however, there may be side effects to this solution such as longer than normal resume times from standby. This solution will only work with external displays such as DFP displays. This driver is not designed to address issues with Local Flat Panel displays or TVs connected to the system. This driver is provided as is. Intel has not tested, and does not warranty, the operation of the driver for this purpose.
Select appropriate operating system and driver to resolve this issue: