Thanks for all the help and advise, the xrandr post did the trick. It would seem that, by simply typing xrandr into a terminal session and it displaying the resolutions available, this sorted it out.
When I went back to screen settings, I have been able to set both monitors to 1680x1050.
Thank you ALL very much
Linux i5-mint16 3.11.0-12-generic #19-Ubuntu SMP Wed Oct 9 16:20:46 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
Intel i5-2320 @3.00 x 4 6Gb GeoForce GT 640 2Gb
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