External screen resolution not listed

I am trying to connect to a MacBook Pro (retina), under Mountain Lion, using VGA, to a 1600x1200@60hz external screen (DELL)...

And I cannot get the proper resolution proposed in the list (the maximum proposed is lower), neither the refresh rate by the way (75 is the only selectable, 60Hz is shown but not selectable).

And yes, I used the option key when clicking on scale to enlarge the list of proposed resolution.

Would the problem be fixed if I would use a DVI cable instead of the VGA adaptor (the screen has indeed the plug...) ? Any solution to make the VGA work ?

Thank you in for your help !